Display Device, Module, and Electronic Device

ABSTRACT

The display defects of a display device are reduced. The display quality of the display device is improved. The display device includes a display panel and a first conductive layer. The display panel includes a display element including a pair of electrodes. An electrode of the pair of electrodes which is closer to one surface of the display panel is supplied with a constant potential. A constant potential is supplied to the first conductive layer. The second conductive layer provided on the other surface of the display panel is in contact with the first conductive layer, whereby the second conductive layer is also supplied with the constant potential. The second conductive layer includes a portion not fixed to the first conductive layer.

This application is a continuation of copending U.S. application Ser.No. 15/743,806, filed on Jan. 11, 2018 which is a 371 National Stageentry of PCT/IB2016/054192 filed on Jul. 14, 2016 which are allincorporated herein by reference.

TECHNICAL FIELD

One embodiment of the present invention relates to a display device, amodule, and an electronic device. In particular, one embodiment of thepresent invention relates to a display device, a module, and anelectronic device that utilize an electroluminescence (hereinafter alsoreferred to as EL) phenomenon.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention include a semiconductor device, a displaydevice, a light-emitting device, a power storage device, a memorydevice, an electronic device, a lighting device, an input device (suchas a touch sensor), and an input/output device (such as a touch panel),and a method for driving any of them and a method for manufacturing anyof them.

BACKGROUND ART

Recent display devices are expected to be used in a variety of uses andbecome diversified.

For example, display devices for mobile devices and the like arerequired to be thin, lightweight, and less likely to be broken.

Light-emitting elements utilizing EL phenomenon (also referred to as ELelements) have features such as ease of thinning and lightening,high-speed response to input signal, and driving with a direct-currentlow voltage source; therefore, application of the light-emittingelements to display devices has been proposed.

For example, Patent Document 1 discloses a flexible light-emittingdevice in which an organic EL element is used.

PRIOR ART DOCUMENT

[Patent Document]

[Patent Document 1] Japanese Published Patent Application No.2014-197522

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When the display panel has a small thickness so as to be lightweight orflexible, the display panel is likely to be influenced by noise.

A factor in causing noise is, for example, a parasitic capacitancebetween the display panel and a housing, a human body, or the like.

For example, when the display panel is changed in shape, the position ofat least one portion of the display panel relative to the housing ischanged in some cases. Thus, parasitic capacitance between the displaypanel and the housing is changed, so that the luminance of the pixelmight be locally changed to cause a display defect.

An object of one embodiment of the present invention is to reducedisplay defects of a display device. Another object of one embodiment ofthe present invention is to improve the display quality of a displaydevice. Another object of one embodiment of the present invention is toprovide a display device with a curved surface. Another object of oneembodiment of the present invention is to provide a flexible displaydevice. Another object of one embodiment of the present invention is toprovide a lightweight display device. Another object of one embodimentof the present invention is to provide a thin display device. Anotherobject of one embodiment of the present invention is to provide adisplay device with high reliability. Another object of one embodimentof the present invention is to provide a novel display device, a novelelectronic device, or the like.

Note that the descriptions of these objects do not disturb the existenceof other objects. In one embodiment of the present invention, there isno need to achieve all the objects. Other objects can be derived fromthe description of the specification, the drawings, and the claims.

Means for Solving the Problems

A display panel of one embodiment of the present invention includes aflexible substrate, a transistor, a light-emitting element, and aconductive layer. The transistor and the light-emitting element are eachpositioned over the flexible substrate. The light-emitting elementincludes a first electrode over the flexible substrate, a layercontaining a light-emitting substance (hereinafter referred to as an ELlayer) over the first electrode, and a second electrode over the ELlayer. The first electrode is electrically connected to a source or adrain of the transistor. The second electrode is supplied with aconstant potential. The transistor and the light-emitting element areeach electrically insulated from the conductive layer. The transistorand the light-emitting element each overlap with the conductive layerwith the flexible substrate provided therebetween. The conductive layeris supplied with a constant potential.

A display device of one embodiment of the present invention includes adisplay panel and a first conductive layer. The display panel hasflexibility. The display panel includes a flexible substrate, atransistor, a light-emitting element, and a second conductive layer. Thetransistor and the light-emitting element are each positioned over theflexible substrate. The light-emitting element includes a firstelectrode over the flexible substrate, an EL layer over the firstelectrode, and a second electrode over the EL layer. The first electrodeis electrically connected to a source or a drain of the transistor. TheEL layer contains a light-emitting substance. The second electrode issupplied with a constant potential. The transistor and thelight-emitting element are each electrically insulated from the secondconductive layer. The transistor and the light-emitting element eachoverlap with the second conductive layer with the flexible substrateprovided therebetween. The second conductive layer comprises a portionin contact with the first conductive layer. The second conductive layercomprises a portion not fixed to the first conductive layer. The firstconductive layer is supplied with a constant potential.

The first conductive layer is preferably in contact with a wiringsupplied with the constant potential in a portion not overlapping withthe display panel.

The area where the second conductive layer and a display region of thedisplay panel overlap with each other is preferably greater than orequal to 80% and less than or equal to 100% of the area of the displayregion.

The area of the second conductive layer is preferably larger than thearea of the display region of the display panel.

The area where the first conductive layer and the display panel overlapwith each other is preferably greater than or equal to 80% and less thanor equal to 100% of the area of the display panel.

The area of the first conductive layer is preferably larger than thearea of the display panel.

The display device preferably includes an insulating layer whichoverlaps with the display panel with the first conductive layer providedtherebetween. For example, the insulating layer preferably contains aresin. The display device may include, for example, a film or a sheetincluding a stack of the insulating layer and the first conductivelayer. The thickness of the film or the sheet is greater than or equalto 20 μm and less than or equal to 100 μm. The Rockwell hardness of theinsulating layer is preferably higher than or equal to M60 and lowerthan or equal to M120 when the insulating layer contains the resin.

The thickness of the display panel is preferably greater than or equalto 50 μm and less than or equal to 100 μm.

In the case where the light-emitting element emits light toward theflexible substrate side, the first conductive layer and the secondconductive layer each have a function of transmitting visible light. Inthe case where the light-emitting element emits light toward a sideopposite to the flexible substrate side, the first conductive layerpreferably contains a metal or an alloy.

One embodiment of the present invention is a module including any of thedisplay devices having the above structures. The module is provided witha connector such as a flexible printed circuit (hereinafter alsoreferred to as an FPC) or a TCP (tape carrier package) or is mountedwith an integrated circuit (IC) by a COG (chip on glass) method, a COF(chip on film) method, or the like.

In one embodiment of the present invention, the above structures may beapplied to a light-emitting device or an input/output device (e.g., atouch panel) instead of the display device.

One embodiment of the present invention is an electronic deviceincluding the above-described module and a sensor. The sensor overlapswith the display panel with the second conductive layer providedtherebetween.

One embodiment of the present invention is an electronic deviceincluding the above-mentioned module and at least one of an antenna, abattery, a housing, a camera, a speaker, a microphone, and an operationbutton.

Effect of the Invention

According to one embodiment of the present invention, display defects ofa display device can be reduced. According to one embodiment of thepresent invention, the display quality of a display device can beimproved. According to one embodiment of the present invention, adisplay device having a curved surface can be provided. According to oneembodiment of the present invention, a display device having flexibilitycan be provided. According to one embodiment of the present invention, alightweight display device can be provided. According to one embodimentof the present invention, a thin display device can be provided.According to one embodiment of the present invention, a display devicewith high reliability can be provided. According to one embodiment ofthe present invention, a novel display device, a novel electronicdevice, or the like can be provided.

Note that the description of these effects does not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily have all the effects listed above. Other effects can bederived from the description of the specification, the drawings, and theclaims.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A-1C Cross-sectional views illustrating an example of a displaypanel.

FIGS. 2A-2D Cross-sectional views illustrating an example of a displaypanel.

FIGS. 3A-3B A circuit diagram of a pixel and a cross-sectional viewillustrating an example of a display panel.

FIGS. 4A-4C Cross-sectional views illustrating an example of a displaypanel.

FIGS. 5A-5C A top view and bottom views illustrating examples of adisplay panel.

FIGS. 6A-6D Top views and cross-sectional views illustrating examples ofa display device.

FIGS. 7A-7D Side views illustrating examples of a display device.

FIG. 8 A cross-sectional view illustrating an example of a displaypanel.

FIGS. 9A-9C Cross-sectional views illustrating an example of a methodfor manufacturing a display panel.

FIGS. 10A-10B Cross-sectional views illustrating an example of a methodfor manufacturing a display panel.

FIGS. 11A-11B Cross-sectional views illustrating an example of a methodfor manufacturing a display panel.

FIGS. 12A-12B Cross-sectional views illustrating examples of a displaypanel.

FIGS. 13A-13B Cross-sectional views illustrating examples of a displaypanel.

FIGS. 14A-14B Perspective views illustrating an example of a touchpanel.

FIG. 15 A cross-sectional view illustrating an example of a touch panel.

FIGS. 16A-16D A cross-sectional view illustrating an example of a touchpanel and a top view and cross-sectional views of a transistor.

FIG. 17 A cross-sectional view illustrating an example of a touch panel.

FIG. 18 A cross-sectional view illustrating an example of a touch panel.

FIG. 19 A cross-sectional view illustrating an example of a touch panel.

FIGS. 20A-20B Perspective views illustrating an example of a touchpanel.

FIG. 21 A cross-sectional view illustrating an example of a touch panel.

FIGS. 22A-22B Cross-sectional views illustrating examples of a touchpanel.

FIGS. 23A-23E Perspective views illustrating examples of an electronicdevice.

FIGS. 24A-24D Top views and bottom views illustrating examples of anelectronic device.

FIGS. 25A-25C Top views illustrating examples of an electronic device.

FIGS. 26A-26C Perspective views illustrating an example of an electronicdevice.

FIG. 27 A perspective view illustrating an example of an electronicdevice.

FIGS. 28A-28D Diagrams illustrating examples of an electronic device.

FIGS. 29A-29H Diagrams illustrating examples of an electronic device.

FIGS. 30A-30D Diagrams illustrating examples of an electronic device.

FIGS. 31A-31E Diagrams illustrating examples of an electronic device.

FIGS. 32A-32C Photographs showing a display device of Example.

FIGS. 33A-33B Photographs of a display device displaying an image inExample.

FIG. 34 A diagram showing measurement results of XRD spectra of samples.

FIGS. 35A-35L TEM images of samples and electron diffraction patterns.

FIGS. 36A-36C Diagrams showing EDX mapping images of a sample.

MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to the drawings.Note that the present invention is not limited to the followingdescription. It will be readily appreciated by those skilled in the artthat modes and details of the present invention can be modified invarious ways without departing from the spirit and scope of the presentinvention. Thus, the present invention should not be construed as beinglimited to the description in the following embodiments.

Note that in structures of the present invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals in different drawings, and a description thereofis not repeated. Further, the same hatching pattern is applied toportions having similar functions, and the portions are not especiallydenoted by reference numerals in some cases.

The position, size, range, or the like of each structure illustrated indrawings is not accurately represented in some cases for easyunderstanding. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film”. Also,the term “insulating film” can be changed into the term “insulatinglayer”.

Note that in this specification, a “substrate” preferably has a functionof supporting at least one of a functional circuit, a functionalelement, a functional film, and the like. A “substrate” does notnecessarily have a function of supporting these objects, and may have afunction of protecting a surface of a device or a panel, or a functionof sealing at least one of a functional circuit, a functional element, afunctional film, and the like, for example. In this specification, asubstrate having flexibility is referred to as a “flexible substrate”.

Embodiment 1

In this embodiment, a display device of one embodiment of the presentinvention will be described with reference to FIG. 1 to FIG. 7.

In this embodiment, an example where an organic EL element is mainlyused is described. An organic EL element is preferable because of theease of being flexible.

FIG. 1 is cross-sectional views of a display panel of one embodiment ofthe present invention and FIG. 2 is cross-sectional views of a displaydevice of one embodiment of the present invention. FIG. 3(A) is acircuit diagram showing an example of a pixel circuit of a displaypanel. FIG. 3(B) and FIG. 4 are cross-sectional views of comparativedisplay panels.

A pixel circuit illustrated in FIG. 3(A) includes a light-emittingelement 31, a transistor 32, a transistor 33, and a capacitor 34. Thetransistor 32 functions as a driving transistor. The transistor 33functions as a selection transistor.

A first electrode of the light-emitting element 31 is electricallyconnected to a first wiring 11. A second electrode of the light-emittingelement 31 is electrically connected to a first electrode of thetransistor 32. A second electrode of the transistor 32 is electricallyconnected to a second wiring 12. A gate of the transistor 32 iselectrically connected to a first electrode of the transistor 33 and afirst electrode of the capacitor 34. A second electrode of thetransistor 33 is electrically connected to a third wiring 13. A gate ofthe transistor 33 is electrically connected to a fourth wiring 14. Asecond electrode of the capacitor 34 is electrically connected to afifth wiring 15.

A comparative display panel 16 illustrated in FIG. 3(B) includes aflexible substrate 51, a layer 20 including a transistor, alight-emitting element 31, an insulating layer 53, a bonding layer 55,and a flexible substrate 57.

The layer 20 including a transistor includes a plurality of conductivelayers such as a gate, a source, and a drain of the transistor and awiring. In FIG. 3(B), a conductive layer 21, which is one of theconductive layers included in the layer 20 including a transistor, isillustrated.

The light-emitting element 31 includes an electrode 41, an EL layer 43,and an electrode 45. The light-emitting element 31 is sealed with theflexible substrate 51, the bonding layer 55, and the flexible substrate57.

One of the electrode 41 and the electrode 45 functions as an anode andthe other functions as a cathode. When a voltage higher than thethreshold voltage of the light-emitting element 31 is applied betweenthe electrode 41 and the electrode 45, holes are injected to the ELlayer 43 from the anode side and electrons are injected to the EL layer43 from the cathode side. The injected electrons and holes arerecombined in the EL layer 43 and a light-emitting substance containedin the EL layer 43 emits light.

The electrode 41 functions as a pixel electrode and is provided for eachlight-emitting element 31. Two adjacent electrodes 41 are electricallyinsulated from each other by the insulating layer 53. The electrode 45functions as a common electrode and is provided for a plurality oflight-emitting elements 31. The electrode 45 corresponds to an electrodeelectrically connected to the first wiring 11 in FIG. 3(A). A fixedpotential is supplied to the electrode 45.

As the thickness of the display panel 16 is smaller, the display panel16 can be lightweight and flexible, whereas the display panel 16 iseasily affected by noise.

As illustrated in FIG. 3(B), capacitance 39 is formed between a finger99 of a user of the display panel 16 and the conductive layer 21. Whenthe finger 99 moves relatively to the conductive layer 21, a distancebetween the finger 99 and the conductive layer 21 is changed and thecapacitance 39 is also changed.

In addition, FIG. 4(A) shows an example where the display panel 16 isplaced over a housing 98 having conductivity. Parts of the display panel16 are in contact with the housing 98 and the other parts are apart fromthe housing 98. FIG. 4(B) is an enlarged view of a region 22C where thedisplay panel 16 is in contact with the housing 98 in FIG. 4(A). FIG.4(C) is an enlarged view of a region 22D where the display panel 16 isnot in contact with the housing 98 in FIG. 4(A).

The capacitance 39 between the housing 98 and the conductive layer 21 inthe case where the housing 98 is in contact with the conductive layer 21(capacitance C3 in FIG. 4(B)) differs from that in the case where theyare not in contact with each other (capacitance C4 in FIG. 4(C)). InFIGS. 4(B) and (C), C3 is larger than C4.

The display panel 16 is partly apart from the housing 98 in some caseseven when being placed over the housing 98. Alternatively, when thedisplay panel 16 is changed in shape, the display panel 16 is partlyapart from the housing 98 in some cases. Thus, while the display panel16 is used, the capacitance 39 between the housing 98 and the conductivelayer 21 is changed in some cases.

As illustrated in FIG. 3(A), the capacitance 39 influences the potentialof the node N. As a distance between the conductive layer 21 and thehousing or the human body is shorter, the capacitance 39 becomes larger.As the thickness of the display panel 16 is smaller, the shortestdistance between the conductive layer 21 and the housing or the humanbody becomes shorter and large capacitance is easily generated. That is,the range of the change of the capacitance 39 is expanded, and the rangeof the change of the potential of the node N is also expanded. Thus, theluminance of the pixel is locally and largely changed, and a displaydefect might be caused.

Thus, in one embodiment of the present invention, the display panel isprovided with a conductive layer to which a constant potential issupplied. Examples of the constant potential include power supplypotentials such as a low power supply potential (VSS) and a high powersupply potential (VDD), a ground potential (GND potential), a commonpotential, a reference potential, and the like.

A display panel 10 illustrated in FIG. 1(A) differs from the displaypanel 16 illustrated in FIG. 3(A) in including a conductive layer 71overlapping with the conductive layer 21 with the flexible substrate 51provided therebetween. The other structures are the same as those in thedisplay panel 16; thus, detailed description is omitted.

The conductive layer 71 is electrically connected to a wiring 19 whichsupplies a constant potential. The conductive layer 71 is electricallyinsulated from the conductive layer 21 included in the layer 20including the transistor. Since the conductive layer 71 is positioned onthe surface of the display panel 10, the constant potential supplied tothe conductive layer 71 is preferably a GND potential in terms of thesafety. In this embodiment, an example where a GND potential is suppliedto the conductive layer 71 is shown.

A capacitance C1 is generated between the conductive layer 21 and theconductive layer 71. As illustrated in FIGS. 1(B) and (C), even when thedisplay panel 10 is bent, the position of the conductive layer 21relative to the conductive layer 71 is not changed. FIG. 1(C) is anenlarged view of a region 22 in FIG. 1(B). In the two regions 22illustrated in FIG. 1(B), distances between the conductive layer 21 andthe conductive layer 71 are the same and the capacitances C1 generatedbetween the conductive layer 21 and the conductive layer 71 are thesame.

Furthermore, capacitance C2 is formed between the finger 99 and theconductive layer 71. As a distance between the finger 99 and theconductive layer 71 is shorter, the capacitance C2 becomes larger. Whenthe capacitance C2 is changed, the potential of the conductive layer 71is changed and the potential of the conductive layer 21 may also bechanged. However, in one embodiment of the present invention, since theconductive layer 71 is supplied with a constant potential, even when thecapacitance C2 is changed, the potential of the conductive layer 21 isnot changed.

In addition, the display panel 10 includes the electrode 45 to which aconstant potential is supplied. Thus, even if the human body or thehousing is positioned on the flexible substrate 57 side, a change incapacitance between the electrode 45 and the human body or the housingdoes not affect the potential of the conductive layer 21.

As described above, in the display panel of one embodiment of thepresent invention, the conductive layers each of which is supplied withthe constant potential are provided in both an upper layer and a lowerlayer of the layer including the transistor. Thus, a change in thepotential of the conductive layer included in the layer including thetransistor due to the noise from the outside can be suppressed, and thedisplay defects in the display panel can be reduced.

The display panel in which one embodiment of the present invention isused is hardly affected by noise even when the thickness is reduced. Thethickness of the display panel 10 can be, for example, greater than orequal to 30 μm and less than or equal to 300 μm and is preferablygreater than or equal to 50 μm and less than or equal to 200 μm, furtherpreferably greater than or equal to 50 μm and less than or equal to 150μm, and still further preferably greater than or equal to 50 μm and lessthan or equal to 100 μm. To increase the mechanical strength of thedisplay panel 10, the thickness of the display panel 10 is preferablygreater than or equal to 50 μm. Furthermore, to increase the flexibilityof the display panel 10, the thickness of the display panel 10 ispreferably less than or equal to 200 μm and further preferably less thanor equal to 100 μm. For example, in the case where the thickness is lessthan or equal to 100 μm, a display panel which can be subjected tobending operation with a radius of curvature of 1 mm or can be subjectedto bending and unbending operation with a radius of curvature of 5 mm inwhich a flat state and a bent state of a display surface are alternatelyrepeated (e.g., more than 100000 times) can be obtained.

FIG. 2(A) is a cross-sectional view of a display device including thedisplay panel 10 and a conductive layer 73. The display panel 10 has thesame structure as a structure example 1 (FIG. 1(A)); thus, detaileddescription is omitted.

The conductive layer 71 includes a portion in contact with theconductive layer 73. The conductive layer 73 is electrically connectedto the wiring 19 which supplies a constant potential. The constantpotential is supplied to the conductive layer 71 through the conductivelayer 73. The conductive layer 71 is not necessarily fixed to theconductive layer 73. When at least part of the conductive layer 71 is incontact with the conductive layer 73, the constant potential is suppliedto the conductive layer 71.

The capacitance C1 is generated between the conductive layer 21 and theconductive layer 71. As illustrated in FIGS. 2(B) to (D), even when thedisplay panel 10 is bent, the position of the conductive layer 21relative to the conductive layer 71 is not changed.

In FIG. 2(B), part of the display panel 10 is in contact with theconductive layer 71 and the other part is apart from the conductivelayer 71. FIG. 2(C) illustrates a region 22A where the display panel 10in FIG. 2(B) is in contact with the conductive layer 71. FIG. 2(D)illustrates a region 22B where the display panel 10 in FIG. 2(B) is notin contact with the conductive layer 71. In the region 22A and theregion 22B, distances between the conductive layer 21 and the conductivelayer 71 are the same and the capacitances C1 generated between theconductive layer 21 and the conductive layer 71 are the same.

Furthermore, the capacitance C2 is formed between the finger 99 and theconductive layer 73. As a distance between the finger 99 and theconductive layer 73 is shorter, the capacitance C2 becomes larger. Whenthe capacitance C2 is changed, the potentials of the conductive layer 73and the conductive layer 71 are changed and the potential of theconductive layer 21 may also be changed. However, in one embodiment ofthe present invention, since the conductive layer 73 and the conductivelayer 71 are supplied with a constant potential, even when thecapacitance C2 is changed, the potential of the conductive layer 21 isnot changed.

As described above, the conductive layer 73 supplied with the constantpotential and the conductive layer 71 positioned at the surface of thedisplay panel 10 are in contact with each other in at least one portion,whereby the constant potential can be supplied to the conductive layer71.

FIGS. 5(A) and (B) are a top view and a bottom view of the display panel10 illustrated in FIG. 1(A) and the like.

FIG. 5(A) is a view of a front surface (display surface) of the displaypanel 10 (also referred to as a top view of the display panel 10) andFIG. 5(B) is a view of a rear surface (surface opposite to the displaysurface) of the display panel 10 (also referred to as a bottom view ofthe display panel 10).

The display panel 10 includes a display region 81 and a scan line drivercircuit 82. The display region 81 includes a plurality of pixels, aplurality of signal lines, and a plurality of scan lines, and has afunction of displaying an image. The scan line driver circuit 82 has afunction of outputting scan signals to the scan lines included in thedisplay region 81.

In this embodiment, an example where the display panel 10 includes ascan line driver circuit is shown; however, one embodiment of thepresent invention is not limited thereto. The display panel 10 mayinclude one of or both a scan line driver circuit and a signal linedriver circuit or may include none of the scan line driver circuit andthe signal line driver circuit. Furthermore, when the display panel 10has a function as a touch sensor, the display panel 10 may include asensor driver circuit.

In the display panel 10, an IC 84 is mounted on the flexible substrate51 by a mounting method such as a COF method. The IC 84 includes, forexample, any one or more of a signal line driver circuit, a scan linedriver circuit, and a sensor driver circuit. Side surfaces of the IC 84are covered with a resin such as an epoxy resin, whereby the mechanicalstrength of a connection portion of the display panel 10 and the IC 84can be increased. Thus, even when the display panel 10 is bent, a crackis less likely to be generated and the reliability of the display panel10 can be increased. As a resin, for example, a resin used as any of avariety of adhesives can be used.

In addition, an FPC 83 is electrically connected to the display panel10. The IC 84 and the scan line driver circuit are supplied with asignal from the outside via the FPC 83. Furthermore, signals can beoutput to the outside from the IC 84 via the FPC 83.

An IC may be mounted on the FPC 83. For example, an IC including any oneor more of a signal line driver circuit, a scan line driver circuit, anda sensor driver circuit may be mounted on the FPC 83. For example, theIC can be mounted on the FPC 83 by a mounting method such as a COFmethod or a TAB (tape automated bonding) method.

The conductive layer 71 is provided on the rear surface of the displaypanel 10. The conductive layer 71 overlaps with the display region 81.An area where the conductive layer 71 and the display region 81 overlapwith each other is preferably greater than or equal to 80% and less thanor equal to 100%, further preferably greater than or equal to 90% andless than or equal to 100%, still further preferably greater than orequal to 95% and less than or equal to 100% of the area of the displayregion 81. Furthermore, the area of the conductive layer 71 ispreferably larger than the area of the display region 81. An area of thedisplay region 81 which does not overlap with the conductive layer 71 ispreferably smaller, in which case the display panel 10 is less likely tobe affected by noise.

As illustrated in FIG. 5(C), the conductive layer 71 may overlap withthe scan line driver circuit 82.

In FIGS. 5(A) to (C), an example where a conductor 74 is connected tothe conductive layer 71 is shown. A constant potential is supplied tothe conductor 74. The conductor 74 electrically connects a wiringsupplied with a GND potential (also referred to as a GND line) to theconductive layer 71. As the conductor 74, a conductive tape, aconductive wiring, or the like is used. For example, a GND line of apower source such as a battery or a power supply circuit may beelectrically connected to the conductive layer 71 through the conductor74.

As illustrated in FIGS. 5(A) to (C), in the case where thelight-emitting element 31 emits light toward the flexible substrate 57side, the conductive layer 71 is positioned on a rear surface of thedisplay panel (surface opposite to the display surface). When theconductive tape, the conductive wiring, or the like is directlyconnected to the conductive layer 71, steps along the shape of theconductive tape, the conductive wiring, or the like may be generated inthe display panel 10. As the thickness of the display panel 10 issmaller, the steps along the shape become apparent. The display regionis preferably smoother without a large step, in which case a morehighly-attractive image is displayed. Thus, it is preferable that theconnection portion of the conductive layer 71 and the conductor 74 notoverlap with the display region 81.

FIG. 6(A) is a top view of the display device illustrated in FIG. 2(A)and the like. FIG. 6(A) is a view of a front surface (display surface)of the display device and FIG. 6(B) is a cross-sectional view takenalong dashed-dotted line A-B in FIG. 6(A). The display panel 10 has thesame structure as the display panel in FIGS. 5(A) and (B); thus,detailed description is omitted.

In FIG. 6(B), layers which the display panel 10 includes between theflexible substrate 51 and the flexible substrate 57 are collectivelyreferred to as an element layer 72. Specifically, the element layer 72includes the layer 20 including a transistor, the light-emitting element31, the insulating layer 53, the bonding layer 55, and the likeillustrated in FIG. 1(A) and the like.

FIGS. 6(A) and (B) show an example where the conductor 74 is connectedto the conductive layer 73. The conductor 74 is an example of aconductor which electrically connects the GND line to the conductivelayer 73. The conductor 74 is supplied with the GND potential.

As illustrated in FIGS. 6(A) and (B), the connection portion of theconductive layer 73 and the conductor 74 is positioned in a portionwhich does not overlap with the display panel 10. Steps along the shapeof the connection portion are formed at a position apart from thedisplay region 81. Thus, the formation of the steps in the displayregion 81 can be prevented.

As described above, the connection portion of the conductor whichelectrically connects the conductive layer 71 included in the displaypanel 10 to the wiring which supplies a constant potential preferablydoes not overlap with the display region 81, further preferably does notoverlap with the display panel 10. Thus, the formation of steps in thedisplay region 81 can be prevented and the display quality of thedisplay region 81 can be improved.

An area where the conductive layer 73 and the display panel 10 overlapwith each other is preferably greater than or equal to 80% and less thanor equal to 100% of the area of the display panel 10. Furthermore, thearea of the conductive layer 73 is preferably larger than the area ofthe display panel 10. As the thickness of the display panel 10 issmaller, the steps along the shape of other structure placed on the rearsurface side of the display device are easily formed in the displayregion 81. The conductive layer 73 overlaps with one surface of thedisplay region 81, whereby the steps formed in the display region 81 canbe reduced.

FIG. 6(C) is a top view of a display device which differs from theabove-described structures. FIG. 6(C) is a view of a front surface(display surface) of the display device and FIG. 6(D) is across-sectional view taken along dashed-dotted line C-D in FIG. 6(C).The display panel 10 has the same structure as the display panel inFIGS. 5(A) and (B); thus, detailed description is omitted.

Although an example where the conductive layer 73 overlaps with (and isin contact with) the entire surface of the conductive layer 71 is shownin FIGS. 6(A) and (B), a conductive layer supplied with a constantpotential may be in contact with part of the conductive layer 71 asillustrated in FIGS. 6(C) and (D).

The display device illustrated in FIGS. 6(C) and (D) includes thedisplay panel 10, a conductive layer 73 a, and a conductive layer 73 b.The conductive layer 73 a includes a portion in contact with theconductive layer 71. The conductive layer 73 b includes a portion incontact with the conductive layer 71.

In this manner, a plurality of conductive layers in contact with theconductive layer 71 are provided, whereby a high flexibility region anda low flexibility region can be provided in the display device. Theconductive layer 73 a is provided to overlap with a region which issusceptible to bending damage such as the connection portion of the FPC83 and the display panel 10, whereby the flexibility of the portionwhich is susceptible to bending damage is reduced. When the displaypanel 10 is changed in shape, a high flexibility region in which theconductive layers 73 a and 73 b are not provided is easily bent; thus,the portion which is susceptible to bending damage can be prevented frombeing bent with a large curvature, and the reliability of the displaydevice can be increased.

A conductor 74 a is connected to the conductive layer 73 a. Theconductor 74 a is an example of a conductor which electrically connectsthe GND line to the conductive layer 73 a. Similarly, a conductor 74 bis connected to the conductive layer 73 b.

As illustrated in FIGS. 6(C) and (D), the connection portion of theconductive layer 73 a and the conductor 74 a and the connection portionof the conductive layer 73 b and the conductor 74 b are each positionedin a portion which does not overlap with the display panel 10. Stepsalong the shape of the connection portion are formed at a position apartfrom the display region 81. Thus, the formation of the steps in thedisplay region 81 can be prevented.

If the conductive layer 73 and the display panel 10 are completelyfixed, when the display device is changed in shape, compressive stressesor tensile stress is applied to the display panel 10 and the displaypanel 10 might be broken.

Thus, in one embodiment of the present invention, the conductive layer71 included in the display panel 10 has a portion which is not fixed tothe conductive layer 73. Accordingly, when the display device is bent oropened, the position of at least one portion of the display panel 10relative to the conductive layer 73 is changed. In addition, since aneutral plane can be formed in the display panel 10, the display panel10 can be prevented from being broken by power applied to the displaypanel 10. Note that the conductive layer 71 may have a portion fixed tothe conductive layer 73 or is not necessarily fixed to the conductivelayer 73. Furthermore, even if the conductive layer 73 is thick, theneutral plane can be formed in the display panel 10. Thus, an allowablerange of the thickness of the conductive layer 73 is widened.

Note that a neutral plane refers to a plane at which distortion ofstress, such as compressive stress or tensile stress, due to deformationsuch as bending is not caused and a plane which does not expand orcontract.

FIG. 7(A) shows an opened display device. The display device includes astack of the conductive layer 73 and the display panel 10. Here, a sideon which the FPC 83 is connected is a display surface of the displaydevice. FIG. 7(B) shows a display device which is bent so that thedisplay panel 10 is on the inside (hereinafter referred to as “bentinward”). In a portion surrounded by a dotted line in FIG. 7(A), endportions of the conductive layer 73 and the display panel 10 are alignedwith each other; in contrast, in a portion surrounded by a dotted linein FIG. 7(B), the end portions of the conductive layer 73 and thedisplay panel 10 are not aligned with each other. The same applies toFIG. 7(C) which shows a display device which is bent so that the displaypanel 10 is on the outside (hereinafter referred to as “bent outward”).

There are one or a plurality of positions at which the display device isbent. FIG. 7(D) shows a tri-fold display device including one inwardbending portion and one outward bending portion.

The conductive layer 71 and the conductive layer 73 can each have asingle-layer structure or a stacked-layer structure including any ofmetals such as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten or an alloycontaining any of these metals as its main component. Alternatively, foreach of the conductive layer 71 and the conductive layer 73, alight-transmitting conductive material such as indium oxide, indium tinoxide (ITO), indium oxide containing tungsten, indium zinc oxidecontaining tungsten, indium oxide containing titanium, indium tin oxidecontaining titanium, indium zinc oxide, zinc oxide, zinc oxidecontaining gallium, or indium tin oxide containing silicon may be used.Alternatively, a semiconductor such as an oxide semiconductor orpolycrystalline silicon whose resistance is lowered by containing animpurity element or the like, or silicide such as nickel silicide may beused. A film including graphene can be used as well. The film includinggraphene can be formed, for example, by reducing a film containinggraphene oxide which is formed into a film shape. A semiconductor suchas an oxide semiconductor containing an impurity element may be used.Alternatively, the conductive layer 71 and the conductive layer 73 mayeach be formed using a conductive paste of silver, carbon, copper, orthe like or a conductive polymer such as a polythiophene. A conductivepaste is preferable because it is inexpensive. A conductive polymer ispreferable because it is easily applied.

In the case where the conductive layer 71 and the conductive layer 73are positioned on the display surface side of the display panel 10, aseach of the conductive layer 71 and the conductive layer 73, aconductive layer which transmits visible light is used. In the casewhere the conductive layer 71 and the conductive layer 73 are positionedon the side opposite to the display surface, the conductive layer 71 andthe conductive layer 73 do not necessarily have a light-transmittingproperty.

In the case where the conductive layer 71 is formed directly on thesurface of the display panel 10, the thickness of the conductive layer71 is larger than or equal to 1 nm and smaller than or equal to 1000 nm,preferably larger than or equal to 1 nm and smaller than or equal to 100nm, further preferably larger than or equal to 1 nm and smaller than orequal to 50 nm, still further preferably larger than or equal to 1 nmand smaller than or equal to 25 nm. The thickness of the conductivelayer 71 is preferably smaller, in which case internal stress of theconductive layer 71 can be reduced and the display panel 10 is lesslikely to be warped.

As the conductive layer 73, a metal foil, a metal plate, or the like canbe used. In the case where the conductive layer 73 overlaps with thebending portion of the display panel 10, the thickness and hardness ofthe conductive layer 73 are enough to have flexibility.

Furthermore, a film or a sheet of a stacked-layer structure of aninsulating layer and a layer containing a conductive material may beused. The layer containing a conductive material functions as theconductive layer 71 or the conductive layer 73. As the film or the sheetof the stacked-layer structure of the insulating layer and the layercontaining a conductive material, a conductive film and a conductivesheet in which the layer containing a conductive material is providedover a resin film or a resin sheet are given as examples. Specifically,a film, a sheet, and the like in which copper, ITO, graphene, or acarbon nanotube is formed over a polyethylene terephthalate (PET) filmor a polyethylene naphthalate (PEN) film are given as examples.Alternatively, a sheet formed by hardening graphite may be used.Graphite and graphene are preferable because they can each be formed asa thin film and have high conductivity.

The thicknesses of the conductive film, the conductive sheet, and thelike are each preferably larger than or equal to 20 μm and less than orequal to 200 μm, further preferably larger than or equal to 20 μm andless than or equal to 150 μm, further preferably larger than or equal to20 μm and less than or equal to 100 μm. Note that in the case wherethere is no limitation on the degree of flexibility of the conductivesheet, the thickness may be larger than 200 μm.

When local pressure is applied to the display panel 10 due to thecontact with a human nail, a stylus, or the like, the display panel 10may be damaged, and further, may be broken. A member positioned underthe display panel 10 is preferably harder, in which case the change inshape of the display panel 10 is suppressed, and the generation of pinholes in the display panel 10 and the damage to the display panel 10 canbe suppressed. For example, a film in which the layer containing aconductive material (corresponding to the conductive layer 73) is formedover a resin layer having Rockwell hardness of higher than or equal toM60 and lower than or equal to M120 is preferably used. As the resinlayer having Rockwell hardness of higher than or equal to M60 and lowerthan or equal to M120, a PET film is given as an example.

Furthermore, a housing of the display device may function as theconductive layer 73.

For each of the flexible substrates 51 and 57, a material such as glass,quartz, a resin, a metal, an alloy, or a semiconductor thin enough tohave flexibility can be used. The substrate through which light isextracted from the light-emitting element is formed using a materialwhich transmits the light. For example, the thickness of the flexiblesubstrate is preferably greater than or equal to 1 μm and less than orequal to 200 μm, further preferably greater than or equal to 1 μm andless than or equal to 100 μm, still further preferably greater than orequal to 10 μm and less than or equal to 50 μm, and particularlypreferably greater than or equal to 10 μm and less than or equal to 25μm. The thickness and hardness of the flexible substrate are set in therange where mechanical strength and flexibility can be balanced againsteach other. The flexible substrate may have a single-layer structure ora stacked-layer structure.

A resin, which has a specific gravity smaller than that of glass, ispreferably used for the flexible substrate, in which case the displaypanel can be lightweight as compared with the case where glass is used.

The substrate is preferably formed using a material with high toughness.In that case, a display panel with high impact resistance that is lesslikely to be broken can be provided. For example, when a resin substrateor a thin metal or alloy substrate is used, the display panel can belightweight and unlikely to be broken as compared with the case where aglass substrate is used.

A metal material and an alloy material, which have high thermalconductivity, are preferable because they can easily conduct heat to thewhole substrate and accordingly can prevent a local temperature rise inthe display panel. The thickness of a substrate using a metal materialor an alloy material is preferably greater than or equal to 10 μm andless than or equal to 200 μm, further preferably greater than or equalto 20 μm and less than or equal to 50 μm.

There is no particular limitation on a material of the metal substrateor the alloy substrate, but it is preferable to use, for example,aluminum, copper, nickel, or a metal alloy such as an aluminum alloy orstainless steel. Examples of a material for a semiconductor substrateinclude silicon and the like.

Furthermore, when a material with high thermal emissivity is used forthe substrate, the surface temperature of the display panel can beprevented from rising, leading to inhibition of breakage or a decreasein reliability of the display panel. For example, the substrate may havea stacked-layer structure of a metal substrate and a layer with highthermal emissivity (the layer can be formed using a metal oxide or aceramic material, for example).

Examples of materials having flexibility and a light-transmittingproperty include polyester resins such as PET and PEN, apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, a polyethersulfone (PES) resin, polyamide resins (such as nylon and aramid), apolysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin,polytetrafluoroethylene (PTFE), and an ABS resin. In particular, amaterial with a low coefficient of linear expansion is preferred, andfor example, a polyamide imide resin, a polyimide resin, a polyamideresin, or PET can be suitably used. A substrate in which a fibrous bodyis impregnated with a resin (also referred to as a prepreg), a substratewhose linear thermal expansion coefficient is reduced by mixing aninorganic filler with a resin, or the like can also be used.

The flexible substrate may have a stacked-layer structure in which atleast one of a hard coat layer (e.g., a silicon nitride layer) by whicha surface of the device is protected from damage, a layer for dispersingpressure (e.g., an aramid resin layer), and the like is stacked over alayer of any of the above-mentioned materials.

When a glass layer is used for the flexible substrate, a barrierproperty against water and oxygen can be improved, and thus a highlyreliable display panel can be provided.

For example, a flexible substrate in which a glass layer, a bondinglayer, and a resin layer are stacked from the side closer to alight-emitting element can be used. The thickness of the glass layer isgreater than or equal to 20 μm and less than or equal to 200 μm,preferably greater than or equal to 25 μm and less than or equal to 100μm. With such a thickness, the glass layer can have both a high barrierproperty against water and oxygen and high flexibility. The thickness ofthe resin layer is greater than or equal to 10 μm and less than or equalto 200 μm, preferably greater than or equal to 20 μm and less than orequal to 50 μm. By providing such a resin layer, occurrence of a crackand a break in the glass layer can be inhibited and mechanical strengthcan be improved. With the substrate that includes such a compositematerial of a glass material and a resin, a highly reliable flexibledisplay panel can be provided.

For the bonding layer, various curable adhesives such as a photocurableadhesive (e.g., an ultraviolet curable adhesive), a reactive curableadhesive, a thermosetting adhesive, and an anaerobic adhesive can beused. Alternatively, an adhesive sheet or the like may be used.

Furthermore, the bonding layer may include a drying agent. For example,it is possible to use a substance that adsorbs moisture by chemicaladsorption, such as oxide of an alkaline earth metal (e.g., calciumoxide or barium oxide). Alternatively, it is possible to use a substancethat adsorbs moisture by physical adsorption, such as zeolite or silicagel. The drying agent is preferably included because it can preventimpurities such as moisture from entering the functional element,thereby improving the reliability of the display panel.

When a filler with a high refractive index or a light scattering memberis contained in the bonding layer, the efficiency of light extractionfrom the light-emitting element can be improved. For example, titaniumoxide, barium oxide, zeolite, or zirconium can be used.

As the light-emitting element, a self-luminous element can be used, andan element whose luminance is controlled by current or voltage isincluded in the category of the light-emitting element. For example, alight-emitting diode (LED), an organic EL element, an inorganic ELelement, or the like can be used. Any of a variety of display elementscan be used in the display device of one embodiment of the presentinvention. For example, a liquid crystal element, an electrophoreticelement, a display element using MEMS (micro electro mechanicalsystems), or the like may be used.

The light-emitting element may be a top-emission, bottom-emission, ordual-emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

The conductive film that transmits visible light can be formed using,for example, indium oxide, ITO, indium zinc oxide, zinc oxide (ZnO), orzinc oxide containing gallium. Alternatively, a film of a metal materialsuch as gold, silver, platinum, magnesium, nickel, tungsten, chromium,molybdenum, iron, cobalt, copper, palladium, or titanium; an alloycontaining any of these metal materials; or a nitride of any of thesemetal materials (e.g., titanium nitride) can be formed thin so as tohave a light-transmitting property. Alternatively, a stacked film of anyof the above materials can be used as the conductive film. For example,a stacked film of ITO and an alloy of silver and magnesium is preferablyused, in which case conductivity can be increased. Furtheralternatively, graphene or the like may be used.

For the conductive film that reflects visible light, for example, ametal material such as aluminum, gold, platinum, silver, nickel,tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or analloy containing any of these metal materials can be used. Further,lanthanum, neodymium, germanium, or the like may be added to the metalmaterial or the alloy. Furthermore, an alloy containing aluminum (analuminum alloy) such as an alloy of aluminum and titanium, an alloy ofaluminum and nickel, an alloy of aluminum and neodymium, or an alloy ofaluminum, nickel, and lanthanum (Al—Ni—La); or an alloy containingsilver such as an alloy of silver and copper, an alloy of silver,palladium, and copper (also referred to as Ag—Pd—Cu or APC), or an alloyof silver and magnesium may be used. An alloy containing silver andcopper is preferable because of its high heat resistance. Further, whena metal film or a metal oxide film is stacked on and in contact with analuminum alloy film, oxidation of the aluminum alloy film can beprevented. Examples of materials for the metal film or the metal oxidefilm include titanium and titanium oxide. Alternatively, the aboveconductive film that transmits visible light and a film containing ametal material may be stacked. For example, a stacked film of silver andITO or a stacked film of an alloy of silver and magnesium and ITO can beused.

Each of the electrodes can be formed by an evaporation method or asputtering method. Alternatively, a discharging method such as an inkjetmethod, a printing method such as a screen printing method, or a platingmethod may be used.

The EL layer 43 includes at least a light-emitting layer. The EL layer43 may include a plurality of light-emitting layers. In addition to thelight-emitting layer, the EL layer 43 may further include one or morelayers containing any of a substance with a high hole-injectionproperty, a substance with a high hole-transport property, ahole-blocking material, a substance with a high electron-transportproperty, a substance with a high electron-injection property, asubstance with a bipolar property (a substance with a high electron- andhole-transport property), and the like.

For the EL layer 43, either a low molecular compound or a high molecularcompound can be used, and an inorganic compound may also be used. Eachof the layers included in the EL layer 43 can be formed by any of thefollowing methods: an evaporation method (including a vacuum evaporationmethod), a transfer method, a printing method, an ink-jet method, acoating method, and the like.

The light-emitting element 31 may contain two or more kinds oflight-emitting substances. Thus, for example, a light-emitting elementthat emits white light can be achieved. For example, light-emittingsubstances are selected so that two or more kinds of light-emittingsubstances emit complementary colors to obtain white light emission. Alight-emitting substance that emits red (R) light, green (G) light, blue(B) light, yellow (Y) light, or orange (O) light or a light-emittingsubstance that emits light containing spectral components of two or moreof R light, G light, and B light can be used, for example. Alight-emitting substance that emits blue light and a light-emittingsubstance that emits yellow light may be used, for example. At thistime, the emission spectrum of the light-emitting substance that emitsyellow light preferably contains spectral components of G light and Rlight. The emission spectrum of the light-emitting element 31 preferablyhas two or more peaks in the wavelength range in a visible region (e.g.,greater than or equal to 350 nm and less than or equal to 750 nm orgreater than or equal to 400 nm and less than or equal to 800 nm).

Moreover, the light-emitting element 31 may be a single elementincluding one EL layer or a tandem element in which EL layers arestacked with a charge generation layer provided therebetween.

In one embodiment of the present invention, a light-emitting elementcontaining an inorganic compound such as a quantum dot may be employed.Examples of quantum dot materials include a colloidal quantum dotmaterial, an alloyed quantum dot material, a core-shell quantum dotmaterial, and a core quantum dot material. For example, an element suchas cadmium (Cd), selenium (Se), zinc (Zn), sulfur (S), phosphorus (P),indium (In), tellurium (Te), lead (Pb), gallium (Ga), arsenic (As), oraluminum (Al) may be contained.

The structure of the transistors in the display panel is notparticularly limited. For example, a planar transistor, a forwardstaggered transistor, or an inverted staggered transistor may be used. Atop-gate transistor or a bottom-gate transistor may be used. Gateelectrodes may be provided above and below a channel.

There is no particular limitation on the crystallinity of asemiconductor material used for the transistors, and an amorphoussemiconductor or a semiconductor having crystallinity (amicrocrystalline semiconductor, a polycrystalline semiconductor, asingle crystal semiconductor, or a semiconductor partly includingcrystal regions) may be used. It is preferable that a semiconductorhaving crystallinity be used, in which case deterioration of thetransistor characteristics can be suppressed.

A semiconductor material used for the semiconductor layer of thetransistor is not particularly limited, and for example, a Group 14element, a compound semiconductor, or an oxide semiconductor can beused. Typically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

An oxide semiconductor is preferably used as a semiconductor where achannel of the transistor is formed. In particular, an oxidesemiconductor having a wider band gap than silicon is preferably used. Asemiconductor material having a wider band gap and a lower carrierdensity than silicon is preferably used because off-state current of thetransistor can be reduced.

For example, the oxide semiconductor preferably contains at least indium(In) or zinc (Zn). Further preferably, the oxide semiconductor containsan oxide represented by an In-M-Zn oxide (M is a metal such as Al, Ti,Ga, Ge, Y, Zr, Sn, La, Ce, Hf, or Nd).

A c-axis aligned crystalline oxide semiconductor (CAAC-OS) is preferablyused as a semiconductor material for the transistors. Unlike anamorphous semiconductor, the CAAC-OS has few defect states, so that thereliability of the transistor can be improved. Moreover, since no grainboundary is observed in the CAAC-OS, a stable and uniform film can beformed over a large area, and stress that is caused by bending aflexible display device does not easily make a crack in a CAAC-OS film.

The CAAC-OS is a crystalline oxide semiconductor in which c-axes ofcrystals are oriented in a direction substantially perpendicular to thefilm surface. It has been found that oxide semiconductors have a varietyof crystal structures other than a single-crystal structure. An exampleof such structures is a nano-crystal (nc) structure, which is anaggregate of nanoscale microcrystals. The crystallinity of a CAAC-OSstructure is lower than that of a single-crystal structure and higherthan that of an nc structure.

The CAAC-OS has c-axis alignment, its pellets (nanocrystals) areconnected in an a-b plane direction, and the crystal structure hasdistortion. For this reason, the CAAC-OS can also be referred to as anoxide semiconductor including a c-axis-aligned a-b-plane-anchored (CAA)crystal.

An organic insulating material or an inorganic insulating material canbe used for the insulating layers included in the display panel.Examples of resins include an acrylic resin, an epoxy resin, a polyimideresin, a polyamide resin, a polyimide-amide resin, a siloxane resin, abenzocyclobutene-based resin, and a phenol resin. Examples of inorganicinsulating films include a silicon oxide film, a silicon oxynitridefilm, a silicon nitride oxide film, a silicon nitride film, an aluminumoxide film, a hafnium oxide film, an yttrium oxide film, a zirconiumoxide film, a gallium oxide film, a tantalum oxide film, a magnesiumoxide film, a lanthanum oxide film, a cerium oxide film, and a neodymiumoxide film.

For each of the conductive layers included in the display panel, any ofthe above-described materials which can be used for the conductive layer71 and the conductive layer 73 can be used.

As described above, in the display device of this embodiment, even ifthe thickness of the display panel is extremely small, the change inpotential of the conductive layer included in the layer including thetransistor due to noise from the outside can be suppressed and thedisplay defects of the display panel can be reduced. In addition, stepsare not easily formed in the display region and degradation in thedisplay quality can be suppressed. Furthermore, the display panel hasflexibility to have a structure which is less likely to be damaged dueto bending.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 2

In this embodiment, structures and a manufacturing method of the displaypanel of one embodiment of the present invention will be described withreference to FIG. 8 to FIG. 22. In this embodiment, a display panel thatuses an EL element as a display element is described as an example.

In this embodiment, the display panel can have a structure in whichsub-pixels of three colors of red (R), green (G), and blue (B) expressone color, a structure in which sub-pixels of four colors of R, G, B,and white (W) express one color, a structure in which sub-pixels of fourcolors of R, G, B, and yellow (Y) express one color, or the like. Thereis no particular limitation on color elements, and colors other than R,G, B, W, and Y may be used. For example, cyan or magenta may be used.

Structure Example 1

FIG. 8 is a cross-sectional view of a display panel 370 employing acolor filter method and having a top-emission structure.

The display panel 370 includes a conductive layer 390, a flexiblesubstrate 371, a bonding layer 377, an insulating layer 378, a pluralityof transistors, a capacitor 305, a conductive layer 307, an insulatinglayer 312, an insulating layer 313, an insulating layer 314, aninsulating layer 315, a light-emitting element 304, a conductive layer355, a spacer 316, a bonding layer 317, a coloring layer 325, alight-blocking layer 326, a flexible substrate 372, a bonding layer 375,and an insulating layer 376.

The conductive layer 390 is provided in at least a display portion 381.The conductive layer 390 may be provided also in a driver circuitportion 382 and the like. The conductive layer 390 is positioned on theside opposite to the display surface side of the display panel 370, andthus the conductive layer 390 does not necessarily transmit visiblelight.

The driver circuit portion 382 includes a transistor 301. The displayportion 381 includes a transistor 302 and a transistor 303.

Each transistor includes a gate, a gate insulating layer 311, asemiconductor layer, a source, and a drain. The gate and thesemiconductor layer overlap with each other with the gate insulatinglayer 311 provided therebetween. Part of the gate insulating layer 311functions as a dielectric of the capacitor 305. The conductive layerfunctioning as the source or the drain of the transistor 302 serves asone electrode of the capacitor 305.

In FIG. 8, a bottom-gate transistor is illustrated. The structure of thetransistor may be different between the driver circuit portion 382 andthe display portion 381. The driver circuit portion 382 and the displayportion 381 may each include a plurality of kinds of transistors.

The capacitor 305 includes a pair of electrodes and the dielectrictherebetween. The capacitor 305 includes a conductive layer that isformed using the same material and the same step as the gate of thetransistor and a conductive layer that is formed using the same materialand the same step as the source and the drain of the transistor.

The insulating layer 312, the insulating layer 313, and the insulatinglayer 314 are each provided to cover the transistors and the like. Thenumber of the insulating layers covering the transistors and the like isnot particularly limited. The insulating layer 314 functions as aplanarization layer. It is preferable that at least one of theinsulating layer 312, the insulating layer 313, and the insulating layer314 be formed using a material inhibiting diffusion of impurities suchas water and hydrogen. Diffusion of impurities from the outside into thetransistors can be effectively inhibited, leading to improvedreliability of the display panel.

In the case where the insulating layer 314 is formed using an organicmaterial, impurities such as moisture might enter the light-emittingelement 304 and the like from the outside of the display panel throughthe insulating layer 314 exposed at an end portion of the display panel.Deterioration of the light-emitting element 304 due to the entry of animpurity leads to deterioration of the display panel. Thus, asillustrated in FIG. 8, it is preferable that an opening which reaches aninorganic film (here, the insulating layer 313) be formed in theinsulating layer 314 so that an impurity such as moisture entering fromthe outside of the display panel does not easily reach thelight-emitting element 304.

FIG. 12(A) is a cross-sectional view illustrating the case where theopening is not provided in the insulating layer 314. The insulatinglayer 314 is preferably provided in the entire area of the display panelas illustrated in FIG. 12(A), in which case the yield of the separationstep described below can be increased.

FIG. 12(B) is a cross-sectional view illustrating the case where theinsulating layer 314 is not positioned at the end portion of the displaypanel. Since an insulating layer formed using an organic material is notpositioned at the end portion of the display panel in the structure ofFIG. 12(B), entry of impurities into the light-emitting element 304 canbe inhibited.

The light-emitting element 304 includes an electrode 321, an EL layer322, and an electrode 323. The light-emitting element 304 may include anoptical adjustment layer 324. The light-emitting element 304 has atop-emission structure with which light is emitted to the coloring layer325 side.

The transistor, the capacitor, the wiring, and the like are provided tooverlap with a light-emitting region of the light-emitting element 304,whereby an aperture ratio of the display portion 381 can be increased.

One of the electrode 321 and the electrode 323 functions as an anode andthe other functions as a cathode. When a voltage higher than thethreshold voltage of the light-emitting element 304 is applied betweenthe electrode 321 and the electrode 323, holes are injected to the ELlayer 322 from the anode side and electrons are injected to the EL layer322 from the cathode side. The injected electrons and holes arerecombined in the EL layer 322 and a light-emitting substance containedin the EL layer 322 emits light.

The electrode 321 is electrically connected to the source or the drainof the transistor 303, directly or through another conductive layer. Theelectrode 321 functions as a pixel electrode and is provided for eachlight-emitting element 304. Two adjacent electrodes 321 are electricallyinsulated from each other by the insulating layer 315.

The EL layer 322 is a layer containing a light-emitting substance.

The electrode 323 functions as a common electrode and is provided for aplurality of light-emitting elements 304. A fixed potential is suppliedto the electrode 323.

The light-emitting element 304 overlaps with the coloring layer 325 withthe bonding layer 317 provided therebetween. The spacer 316 overlapswith the light-blocking layer 326 with the bonding layer 317 providedtherebetween. Although FIG. 8 illustrates the case where a space isprovided between the light-emitting element 304 and the light-blockinglayer 326, the light-emitting element 304 and the light-blocking layer326 may be in contact with each other. Although the spacer 316 isprovided on the flexible substrate 371 side in the structure illustratedin FIG. 8, the spacer 316 may be provided on the flexible substrate 372side (e.g., in a position closer to the flexible substrate 371 than thatof the light-blocking layer 326).

Owing to the combination of a color filter (the coloring layer 325) anda microcavity structure (the optical adjustment layer 324), light withhigh color purity can be extracted from the display panel. The thicknessof the optical adjustment layer 324 is varied depending on the color ofthe pixel.

The coloring layer is a colored layer that transmits light in a specificwavelength range. For example, a color filter that transmits light in aspecific wavelength range, such as red, green, blue, or yellow light,can be used. Examples of materials that can be used for the coloringlayer include a metal material, a resin material, and a resin materialcontaining a pigment or dye.

Note that one embodiment of the present invention is not limited to acolor filter method, and a separate coloring method, a color conversionmethod, a quantum dot method, and the like may be employed.

The light-blocking layer is provided between the adjacent coloringlayers. The light-blocking layer blocks light emitted from an adjacentlight-emitting element to inhibit color mixture between adjacentlight-emitting elements. Here, the coloring layer is provided such thatits end portion overlaps with the light-blocking layer, whereby lightleakage can be reduced. For the light-blocking layer, a material thatblocks light from the light-emitting element can be used; for example, ablack matrix can be formed using a metal material or a resin materialcontaining pigment or dye. Note that it is preferable to provide thelight-blocking layer in a region other than the pixel, such as thedriver circuit, in which case undesired leakage of guided light or thelike can be suppressed.

An overcoat may be provided to cover the coloring layer and thelight-blocking layer. The overcoat can prevent an impurity and the likecontained in the coloring layer from being diffused into thelight-emitting element. The overcoat is formed with a material thattransmits light emitted from the light-emitting element; for example, itis possible to use an inorganic insulating film such as a siliconnitride film or a silicon oxide film, an organic insulating film such asan acrylic film or a polyimide film, or a stacked layer of an organicinsulating film and an inorganic insulating film.

In the case where a material of the bonding layer is applied to thecoloring layer and the light-blocking layer, a material that has highwettability with respect to the material of the bonding layer ispreferably used as the material of the overcoat. For example, an oxideconductive film such as an ITO film or a metal film such as an Ag filmwhich is thin enough to transmit light is preferably used as theovercoat.

When a material that has high wettability with respect to the materialfor the bonding layer is used as the material of the overcoat, thematerial for the bonding layer can be uniformly applied. Thus, entry ofbubbles in the step of attaching the pair of substrates to each othercan be prevented, and thus a display defect can be prevented.

The insulating layer 378 and the flexible substrate 371 are attached toeach other with the bonding layer 377. The insulating layer 376 and theflexible substrate 372 are attached to each other with the bonding layer375. The insulating layer 376 and the insulating layer 378 arepreferably highly resistant to moisture. The light-emitting element 304,the transistors, and the like are preferably provided between a pair ofinsulating layers which are highly resistant to moisture, in which caseimpurities such as moisture can be prevented from entering theseelements, leading to higher reliability of the display panel.

Examples of the insulating film highly resistant to moisture include afilm containing nitrogen and silicon (e.g., a silicon nitride film and asilicon nitride oxide film) and a film containing nitrogen and aluminum(e.g., an aluminum nitride film). Alternatively, a silicon oxide film, asilicon oxynitride film, an aluminum oxide film, or the like may beused.

For example, the moisture vapor transmission rate of the insulating filmhighly resistant to moisture is lower than or equal to 1×10⁻⁵[g/(m²·day)], preferably lower than or equal to 1×10⁻⁶ [g/(m²·day)],further preferably lower than or equal to 1×10⁻⁷ [g/(m²·day)], stillfurther preferably lower than or equal to 1×10⁻⁸ [g/(m²·day)].

A connection portion 306 includes the conductive layer 307 and theconductive layer 355. The conductive layer 307 and the conductive layer355 are electrically connected to each other. The conductive layer 307can be formed using the same material and the same step as those of thesource and the drain of the transistor. The conductive layer 355 iselectrically connected to an external input terminal through which asignal or a potential from the outside is transmitted to the drivercircuit portion 382. Here, an example in which an FPC 373 is provided asan external input terminal is shown. The FPC 373 and the conductivelayer 355 are electrically connected to each other through a connector319.

As the connector 319, any of various anisotropic conductive films (ACF),anisotropic conductive pastes (ACP), and the like can be used.

<Example of Manufacturing Method of Structure Example 1>

An example of a method for manufacturing the structure example 1 isdescribed with reference to FIG. 9 to FIG. 11. FIG. 9 to FIG. 11 arecross-sectional views illustrating a method for manufacturing thedisplay portion 381 of the display panel 370.

As illustrated in FIG. 9(A), a separation layer 403 is formed over aformation substrate 401. Next, a layer to be separated is formed overthe separation layer 403. Here, the layer to be separated that is formedover the separation layer 403 corresponds to the layers from theinsulating layer 378 to the light-emitting element 304 in FIG. 8.

As the formation substrate 401, a substrate having at least heatresistance high enough to withstand process temperature in amanufacturing process is used. As the formation substrate 401, forexample, a glass substrate, a quartz substrate, a sapphire substrate, asemiconductor substrate, a ceramic substrate, a metal substrate, a resinsubstrate, or a plastic substrate can be used.

Note that it is preferable to use a large-sized glass substrate as theformation substrate 401 in terms of productivity. For example, a glasssubstrate having a size greater than or equal to the 3rd generation (550mm×650 mm) and less than or equal to the 10th generation (2950 mm×3400mm) or a glass substrate having a larger size than the 10th generationis preferably used.

In the case where a glass substrate is used as the formation substrate401, as a base film, an insulating film such as a silicon oxide film, asilicon oxynitride film, a silicon nitride film, or a silicon nitrideoxide film is preferably formed between the formation substrate 401 andthe separation layer 403, in which case contamination from the glasssubstrate can be prevented.

The separation layer 403 can be formed using an element selected fromtungsten, molybdenum, titanium, tantalum, niobium, nickel, cobalt,zirconium, zinc, ruthenium, rhodium, palladium, osmium, iridium, andsilicon; an alloy material containing any of the elements; a compoundmaterial containing any of the elements; or the like. A crystalstructure of a layer containing silicon may be amorphous, microcrystal,or polycrystal. Furthermore, a metal oxide such as aluminum oxide,gallium oxide, zinc oxide, titanium dioxide, indium oxide, indium tinoxide, indium zinc oxide, or an In—Ga—Zn oxide can be used. Theseparation layer 403 is preferably formed using a high-melting-pointmetal material such as tungsten, titanium, or molybdenum, in which casethe degree of freedom of the process for forming the layer to beseparated can be increased.

The separation layer 403 can be formed by, for example, a sputteringmethod, a plasma CVD method, a coating method (including a spin coatingmethod, a droplet discharging method, a dispensing method, and thelike), a printing method, or the like. The thickness of the separationlayer 403 is, for example, greater than or equal to 1 nm and less thanor equal to 200 nm, preferably greater than or equal to 10 nm and lessthan or equal to 100 nm.

In the case where the separation layer 403 has a single-layer structure,a tungsten layer, a molybdenum layer, or a layer containing a mixture oftungsten and molybdenum is preferably formed. Alternatively, a layercontaining an oxide or an oxynitride of tungsten, a layer containing anoxide or an oxynitride of molybdenum, or a layer containing an oxide oran oxynitride of a mixture of tungsten and molybdenum may be formed.Note that the mixture of tungsten and molybdenum is an alloy of tungstenand molybdenum, for example.

In the case where the separation layer 403 is formed to have astacked-layer structure including a layer containing tungsten and alayer containing an oxide of tungsten, the layer containing an oxide oftungsten may be formed as follows: the layer containing tungsten isformed first and an insulating film formed of an oxide is formedthereover, so that the layer containing an oxide of tungsten is formedat the interface between the tungsten layer and the insulating film.Alternatively, the layer containing an oxide of tungsten may be formedby performing thermal oxidation treatment, oxygen plasma treatment,nitrous oxide (N₂O) plasma treatment, treatment with a highly oxidizingsolution such as ozone water, or the like on the surface of the layercontaining tungsten. Plasma treatment or heat treatment may be performedin an atmosphere of oxygen, nitrogen, or nitrous oxide alone, or a mixedgas of any of these gasses and another gas. Surface condition of theseparation layer 403 is changed by the plasma treatment or heattreatment, whereby adhesion between the separation layer 403 and theinsulating film formed later can be controlled.

Note that the separation layer is not necessary in the case whereseparation at the interface between the formation substrate and thelayer to be separated is possible. For example, a glass substrate isused as the formation substrate, and an organic resin such as polyimide,polyester, polyolefin, polyamide, polycarbonate, or acrylic is formed incontact with the glass substrate. Next, adhesion between the formationsubstrate and the organic resin is improved by laser light irradiationor heat treatment. Then, an insulating film, a transistor, and the likeare formed over the organic resin. After that, separation at theinterface between the formation substrate and the organic resin can beperformed by performing laser light irradiation with energy densityhigher than that of the above laser light irradiation or performing heattreatment at a temperature higher than that of the above heat treatment.Moreover, the interface between the formation substrate and the organicresin may be filled with a liquid to perform separation.

The organic resin may be used for a substrate of the device.Alternatively, the organic resin may be removed and another substratemay be attached to an exposed surface of the layer to be separated withthe use of an adhesive.

Alternatively, separation at the interface between a metal layer and theorganic resin may be performed in the following manner: the metal layeris provided between the formation substrate and the organic resin andcurrent is made to flow in the metal layer so that the metal layer isheated.

The insulating layer 378 preferably has a single-layer structure or astacked-layer structure including any of a silicon nitride film, asilicon oxynitride film, a silicon oxide film, a silicon nitride oxidefilm, and the like.

The insulating layer 378 can be formed by a sputtering method, a plasmaCVD method, a coating method, a printing method, or the like. Forexample, the insulating layer 378 is formed at a temperature higher thanor equal to 250° C. and lower than or equal to 400° C. by a plasma CVDmethod, whereby the insulating layer 378 can be a dense film having anexcellent moisture-resistant property. Note that the thickness of theinsulating layer 378 is preferably greater than or equal to 10 nm andless than or equal to 3000 nm, or further preferably greater than orequal to 200 nm and less than or equal to 1500 nm.

As illustrated in FIG. 9(B), a separation layer 413 is formed over aformation substrate 411. Next, a layer to be separated is formed overthe separation layer 413. Here, the layer to be separated that is formedover the separation layer 413 corresponds to the insulating layer 376,the light-blocking layer 326, and the coloring layer 325 in FIG. 8.

The formation substrate 411, the separation layer 413, and theinsulating layer 376 can be forming using the materials that can be usedfor the formation substrate 401, the separation layer 403, and theinsulating layer 378, respectively.

Then, as illustrated in FIG. 9(C), the formation substrate 401 and theformation substrate 411 are attached to each other with the bondinglayer 317.

Then, as illustrated in FIG. 10(A), the formation substrate 401 and theinsulating layer 378 are separated from each other. Note that either ofthe formation substrate 401 and the formation substrate 411 may beseparated first.

Before the separation of the formation substrate 401 and the insulatinglayer 378, a separation starting point is preferably formed using laserlight, a sharp knife, or the like. The insulating layer 378 is partlycracked (or broken), whereby the separation starting point can beformed. For example, laser light irradiation enables part of theinsulating layer 378 to be melted, evaporated, or thermally broken.

Then, the insulating layer 378 and the formation substrate 401 areseparated from the formed separation starting point by physical force(e.g., a separation process with a human hand or a jig, or a separationprocess by rotation of a roller adhered to the substrate). In the lowerpart of FIG. 10(A), the separation layer 403 and the formation substrate401 that are separated from the insulating layer 378 are illustrated.After that, as illustrated in FIG. 10(A), the exposed insulating layer378 and the flexible substrate 371 are attached to each other with thebonding layer 377.

In many cases, both sides of a film that can be favorably used as theflexible substrate 371 are provided with separation films (also referredto as separate films or release films). When the flexible substrate 371and the insulating layer 378 are bonded to each other, it is preferablethat only one separation film which is provided over the flexiblesubstrate 371 be separated, and the other separation film remain. Thisfacilitates transfer and processing in later steps. FIG. 10(A)illustrates an example in which one surface of the flexible substrate371 is provided with a separation film 398.

Then, as illustrated in FIG. 10(B), the formation substrate 411 and theinsulating layer 376 are separated from each other. In the upper part ofFIG. 10(B), the separation layer 413 and the formation substrate 411that are separated from the insulating layer 376 are illustrated. Next,the exposed insulating layer 376 and the flexible substrate 372 areattached to each other with the bonding layer 375. FIG. 10(B)illustrates an example in which one surface of the flexible substrate372 is provided with a separation film 399.

Next, as illustrated in FIG. 11(A), the peeling film 398 is peeled, andthe conductive layer 390 is formed on the surface of the exposedflexible substrate 371.

Then, as illustrated in FIG. 11(B), the peeling film 399 is peeled. Thepeeling film 399 is preferably peeled after the formation of theconductive layer 390. When the conductive layer 390 is formed in thestate of including the peeling film 399, the warp of the display paneldue to internal stress of the conductive layer 390 can be suppressed.

As described above, in one embodiment of the present invention, each ofthe functional elements and the like included in the display panel isformed over the formation substrate; thus, even in the case where ahigh-resolution display panel is manufactured, high alignment accuracyof the flexible substrate is not required. It is thus easy to attach theflexible substrate. In addition, since the functional element and thelike can be fabricated with high temperatures, a highly reliable displaypanel can be obtained.

Structure Example 2

FIG. 13(A) shows a cross-sectional view of a display panel employing acolor filter method. Note that in the following structure examples,components similar to those in the above structure example will not bedescribed in detail.

The display panel in FIG. 13(A) includes a conductive layer 380, theflexible substrate 371, the bonding layer 377, the insulating layer 378,a plurality of transistors, the conductive layer 307, the insulatinglayer 312, the insulating layer 313, the insulating layer 314, theinsulating layer 315, the light-emitting element 304, the conductivelayer 355, the bonding layer 317, the coloring layer 325, the flexiblesubstrate 372, and the insulating layer 376.

The conductive layer 380 is provided in at least the display portion381. The conductive layer 380 may be provided also in a driver circuitportion 382 and the like. The conductive layer 380 is positioned on thedisplay surface of the display panel, and thus the conductive layer 380is formed using a material which transmits visible light.

The driver circuit portion 382 includes the transistor 301. The displayportion 381 includes the transistor 303.

Each transistor includes two gates, the gate insulating layer 311, asemiconductor layer, a source, and a drain. The two gates each overlapwith the semiconductor layer with the gate insulating layer 311 providedtherebetween. FIG. 13(A) illustrates an example where each transistorhas a structure in which the semiconductor layer is sandwiched betweenthe two gates. Such transistors can have higher field-effect mobilityand thus have higher on-state current than other transistors.Consequently, a circuit capable of high-speed operation can be obtained.Furthermore, the area occupied by a circuit can be reduced. The use ofthe transistor having high on-state current can reduce signal delay inwirings and can reduce display luminance variation even in a displaypanel in which the number of wirings is increased because of an increasein size or resolution. FIG. 13(A) illustrates an example in which one ofthe gates is formed using the same material and the same step as theelectrode 321.

The light-emitting element 304 has a bottom-emission structure withwhich light is emitted to the coloring layer 325 side.

The light-emitting element 304 overlaps with the coloring layer 325 withthe insulating layer 314 provided therebetween. The coloring layer 325is provided between the light-emitting element 304 and the flexiblesubstrate 371. FIG. 13(A) illustrates an example in which the coloringlayer 325 is provided over the insulating layer 313. In the exampleillustrated in FIG. 13(A), a light-blocking layer and a spacer are notprovided.

Structure Example 3

FIG. 13(B) shows a cross-sectional view of a display panel employing aseparate coloring method.

The display panel in FIG. 13(B) includes the conductive layer 390, theflexible substrate 371, the bonding layer 377, the insulating layer 378,a plurality of transistors, the conductive layer 307, the insulatinglayer 312, the insulating layer 313, the insulating layer 314, theinsulating layer 315, the spacer 316, the light-emitting element 304,the bonding layer 317, the flexible substrate 372, and the insulatinglayer 376.

FIG. 13(B) shows an example where the conductive layer 390 is providedover the entire surface of the flexible substrate 371.

The driver circuit portion 382 includes a transistor 301. The displayportion 381 includes the transistor 302, the transistor 303, and thecapacitor 305.

Each transistor includes two gates, the gate insulating layer 311, asemiconductor layer, a source, and a drain. The two gates each overlapwith the semiconductor layer with the insulating layer providedtherebetween. FIG. 13(B) illustrates an example where each transistorhas a structure in which the semiconductor layer is sandwiched betweenthe two gates. In the example illustrated in FIG. 13(B), one of thegates is formed between the insulating layer 313 and the insulatinglayer 314.

The light-emitting element 304 has a top-emission structure with whichlight is emitted to the flexible substrate 372 side. FIG. 13(B) shows anexample where the light-emitting element 304 does not include an opticaladjustment layer. The insulating layer 376 serves as a sealing layer forthe light-emitting element 304.

The connection portion 306 includes the conductive layer 307. Theconductive layer 307 is electrically connected to the FPC 373 throughthe connector 319.

Application Example

In one embodiment of the present invention, a display device providedwith a touch sensor (also referred to as a touch panel) can bemanufactured.

There is no particular limitation on a sensor element included in thetouch panel of one embodiment of the present invention. Note that avariety of sensors that can sense proximity or touch of a sensing targetsuch as a finger or a stylus can be used as the sensor element.

For example, a variety of types such as a capacitive type, a resistivetype, a surface acoustic wave type, an infrared type, an optical type,and a pressure-sensitive type can be used for the sensor.

In this embodiment, a touch panel including a capacitive sensor elementwill be described as an example.

Examples of the capacitive sensor element include a surface capacitivesensor element and a projected capacitive sensor element. Examples ofthe projected capacitive sensor element include a self-capacitive sensorelement and a mutual capacitive sensor element. The use of a mutualcapacitive sensor element is preferable because multiple points can besensed simultaneously.

The touch panel of one embodiment of the present invention can have anyof a variety of structures, including a structure in which a displaypanel and a sensor element that are separately formed are attached toeach other and a structure in which an electrode and the like includedin a sensor element are provided on one or both of a substratesupporting a display element and a counter substrate.

Structure Example 4

FIG. 14(A) is a schematic perspective view of a touch panel 300. FIG.14(B) is a developed view of the schematic perspective view of FIG.14(A). Note that only typical components are illustrated for simplicity.In FIG. 14(B), some components (such as the flexible substrate 330 andthe flexible substrate 372) are illustrated only in dashed outline.

The touch panel 300 includes an input device 310 and the display panel370, which are provided to overlap with each other.

The input device 310 includes the flexible substrate 330, an electrode331, an electrode 332, a plurality of wirings 341, and a plurality ofwirings 342. An FPC 350 is electrically connected to each of theplurality of wirings 341 and the plurality of wirings 342. The FPC 350is provided with an IC 351.

The display panel 370 includes the flexible substrate 371 and theflexible substrate 372 which are provided so as to face each other. Thedisplay panel 370 includes the display portion 381 and the drivercircuit portion 382. A wiring 383 and the like are provided over theflexible substrate 371. The FPC 373 is electrically connected to thewiring 383. The FPC 373 is provided with an IC 374.

The wiring 383 has a function of supplying a signal and power to thedisplay portion 381 and the driver circuit portion 382. The signal andpower are input to the wiring 383 from the outside or the IC 374 throughthe FPC 373.

FIG. 15 illustrates an example of a cross-sectional view of the touchpanel 300. FIG. 15 shows cross-sectional structures of the displayportion 381, the driver circuit portion 382, the region including theFPC 373, the region including the FPC 350, and the like. Furthermore,FIG. 15 illustrates a cross-sectional structure of a crossing portion387 where a wiring formed by processing a conductive layer used forforming the gate of the transistor and a wiring formed by processing aconductive layer used for forming the source and the drain of thetransistor cross each other.

The flexible substrate 371 and the flexible substrate 372 are attachedto each other with the bonding layer 317. The flexible substrate 372 andthe flexible substrate 330 are attached to each other with a bondinglayer 396. Here, the layers from the flexible substrate 371 to theflexible substrate 372 correspond to the display panel 370. Furthermore,the layers from the flexible substrate 330 to the electrode 334correspond to the input device 310. In other words, the bonding layer396 attaches the display panel 370 and the input device 310 to eachother. Alternatively, the layers from the flexible substrate 371 to theinsulating layer 376 correspond to the display panel 370. Furthermore,the layers from the flexible substrate 330 to the flexible substrate 372correspond to the input device 310. In other words, the bonding layer375 attaches the display panel 370 and the input device 310 to eachother.

The structure of the display panel 370 shown in FIG. 15 is similar tothat of the display panel shown in FIG. 8 and is thus not described indetail.

<Input Device 310>

On the flexible substrate 372 side of the flexible substrate 330, theelectrode 331 and the electrode 332 are provided. An example where theelectrode 331 includes an electrode 333 and the electrode 334 isdescribed here. As illustrated in the crossing portion 387 in FIG. 15,the electrodes 332 and 333 are formed on the same plane. An insulatinglayer 395 is provided to cover the electrode 332 and the electrode 333.The electrode 334 electrically connects two electrodes 333, betweenwhich the electrode 332 is provided, through openings formed in theinsulating layer 395.

In a region near the end portion of the flexible substrate 330, aconnection portion 308 is provided. The connection portion 308 has astack of a wiring 342 and a conductive layer formed by processing aconductive layer used for forming the electrode 334. The connectionportion 308 is electrically connected to the FPC 350 through a connector309.

The flexible substrate 330 is attached to the insulating layer 393 withthe bonding layer 391. As in the manufacturing method for the structureexample 1, the input device 310 can also be manufactured by formingelements over a formation substrate, separating the formation substrate,and then transferring the elements over the flexible substrate 330.Alternatively, the insulating layer 393, the elements, and the like maybe directly formed on the flexible substrate 330 (see FIG. 16A).

Structure Example 5

The touch panel shown in FIG. 16(A) is different from the touch panel inFIG. 15 in the structures of the transistors 301, 302, and 303 and thecapacitor 305 and in not including the bonding layer 391.

FIG. 16(A) illustrates a top-gate transistor.

Each transistor includes a gate, the gate insulating layer 311, asemiconductor layer, a source, and a drain. The gate and thesemiconductor layer overlap with each other with the gate insulatinglayer 311 provided therebetween. The semiconductor layer may includelow-resistance regions 348. The low-resistance regions 348 function asthe source and drain of the transistor.

The conductive layer over the insulating layer 313 functions as a leadwiring. The conductive layer is electrically connected to the region 348through an opening provided in the insulating layer 313, the insulatinglayer 312, and the gate insulating layer 311.

In FIG. 16(A), the capacitor 305 has a stacked-layer structure thatincludes a layer formed by processing a semiconductor layer used forforming the above-described semiconductor layer, the gate insulatinglayer 311, and a layer formed by processing a conductive layer used forforming the gate. Here, part of the semiconductor layer of the capacitor305 preferably has a region 349 having a higher conductivity than aregion 347 where the channel of the transistor is formed.

The region 348 and the region 349 each can be a region containing moreimpurities than the region 347 where the channel of the transistor isformed, a region with a high carrier concentration, a region with lowcrystallinity, or the like.

A transistor 848 illustrated in FIGS. 16(B) to (D) can be used in thedisplay device of one embodiment of the present invention.

FIG. 16(B) is a top view of the transistor 848. FIG. 16(C) is across-sectional view in the channel length direction of the transistor848 in the display device of one embodiment of the present invention.The cross section of the transistor 848 illustrated in FIG. 16(C) istaken along the dashed-dotted line X1-X2 in FIG. 16(B). FIG. 16(D) is across-sectional view in the channel width direction of the transistor848 in the display device of one embodiment of the present invention.The cross section of the transistor 848 illustrated in FIG. 16(D) istaken along the dashed-dotted line Y1-Y2 in FIG. 16(B).

The transistor 848 is a type of top-gate transistor including a backgate.

In the transistor 848, a semiconductor layer 742 is formed over aprojection of an insulating layer 772. When the semiconductor layer 742is provided over the projection of the insulating layer 772, the sidesurface of the semiconductor layer 742 can also be covered with a gate743. Thus, the transistor 848 has a structure in which the semiconductorlayer 742 can be electrically surrounded by an electric field of thegate 743. Such a structure of a transistor in which a semiconductor filmin which a channel is formed is electrically surrounded by an electricfield of a conductive film is called a surrounded channel (s-channel)structure. A transistor with an s-channel structure is referred to as an“s-channel-type transistor” or an “s-channel transistor”.

In the s-channel structure, a channel can be formed in the whole (bulk)of the semiconductor layer 742. In the s-channel structure, the draincurrent of the transistor can be increased, so that a larger amount ofon-state current can be obtained. Furthermore, the entire channelformation region of the semiconductor layer 742 can be depleted by theelectric field of the gate 743. Accordingly, the off-state current ofthe transistor with the s-channel structure can further be reduced.

A back gate 723 is provided over the insulating layer 378.

A conductive layer 744 a provided over an insulating layer 729 iselectrically connected to the semiconductor layer 742 through an opening747 c formed in the gate insulating layer 311, an insulating layer 728,and the insulating layer 729. A conductive layer 744 b provided over theinsulating layer 729 is electrically connected to the semiconductorlayer 742 through an opening 747 d formed in the gate insulating layer311 and the insulating layers 728 and 729.

The gate 743 provided over the gate insulating layer 311 is electricallyconnected to the back gate 723 through an opening 747 a and an opening747 b formed in the gate insulating layer 311 and the insulating layer772. Accordingly, the same potential is supplied to the gate 743 and theback gate 723. Furthermore, either or both of the opening 747 a and theopening 747 b may be omitted. In the case where both the opening 747 aand the opening 747 b are omitted, different potentials can be suppliedto the back gate 723 and the gate 743.

As a semiconductor in the transistor having the s-channel structure, anoxide semiconductor, silicon such as polycrystalline silicon or singlecrystal silicon that is transferred from a single crystal siliconsubstrate, or the like is used.

Structure Example 6

FIG. 17 shows an example of a touch panel in which a bottom-emissiondisplay panel and an input device are attached to each other with thebonding layer 396.

FIG. 17 shows an example where the conductive layer 380 is provided notonly in the display portion 381, but also in the driver circuit portion382 and in an end portion of the flexible substrate 371 which overlapswith the FPC 373.

The display panel in FIG. 17 is different from that in FIG. 13(A) inthat an insulating layer 376 is included. The input device in FIG. 17 isdifferent from that in FIG. 16 in that the insulating layer 393 is notprovided and that the electrode 331, the electrode 332, and the like areprovided directly on the flexible substrate 330.

Structure Example 7

FIG. 18 shows an example of a touch panel in which a display panel usinga separate coloring method and an input device are attached to eachother with the bonding layer 375.

The display panel in FIG. 18 has a structure similar to that in FIG.13(B).

The input device in FIG. 18 includes the insulating layer 376 over aflexible substrate 392, and the electrode 334 and the wiring 342 overthe insulating layer 376. The electrode 334 and the wiring 342 arecovered with the insulating layer 395. The electrode 332 and theelectrode 333 are provided over the insulating layer 395. The flexiblesubstrate 330 is attached to the flexible substrate 392 with the bondinglayer 396.

Structure Example 8

FIG. 19 shows an example in which a touch sensor and the light-emittingelement 304 are provided between a pair of flexible substrates (theflexible substrate 371 and the flexible substrate 372). When twoflexible substrates are used, the touch panel can be thin, lightweight,and flexible.

The structure in FIG. 19 can be fabricated by changing the structure ofthe layer to be separated that is formed over the formation substrate411 in the manufacturing process example for the structure example 1. Inthe manufacturing process example for the structure example 1, as thelayer to be separated that is formed over the formation substrate 411,the insulating layer 376, the coloring layer 325, and the light-blockinglayer 326 are formed (FIG. 9(B)).

In the case where the structure in FIG. 19 is fabricated, after theinsulating layer 376 is formed, the electrode 332, the electrode 333,and the wiring 342 are formed over the insulating layer 376. Then, theinsulating layer 395 covering these electrodes is formed. Next, theelectrode 334 is formed over the insulating layer 395. Then, theinsulating layer 327 covering the electrode 334 is formed. After that,the coloring layer 325 and the light-blocking layer 326 are formed overthe insulating layer 327. Then, attachment to the formation substrate401 is performed, the formation substrates are separated, and theflexible substrate is attached; thus, the touch panel having thestructure in FIG. 19 can be fabricated.

Structure Example 9

FIGS. 20(A) and (B) are schematic perspective views of a touch panel320.

In FIGS. 20(A) and (B), the flexible substrate 372 of a display panel379 is provided with an input device 318. The wiring 341, the wiring342, and the like of the input device 318 are electrically connected tothe FPC 373 provided for the display panel 379.

With the above structure, the FPC connected to the touch panel 320 canbe provided only on one substrate side (on the flexible substrate 371side in this embodiment). Although two or more FPCs may be attached tothe touch panel 320, it is preferable that the touch panel 320 beprovided with one FPC 373 and signals be supplied from the FPC 373 toboth the display panel 379 and the input device 318 as illustrated inFIGS. 20(A) and (B), for the simplicity of the structure.

The IC 374 may have a function of driving the input device 318.Alternatively, an IC for driving the input device 318 may further beprovided. Further alternatively, an IC for driving the input device 318may be mounted on the flexible substrate 371.

FIG. 21 is a cross-sectional view showing a region including the FPC373, a connection portion 385, the driver circuit portion 382, and thedisplay portion 381 in FIG. 20.

In the connection portion 385, one of the wirings 342 (or the wirings341) and one of the conductive layers 307 are electrically connected toeach other through a connector 386.

As the connector 386, a conductive particle can be used, for example. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. It is preferable to usenickel or gold as the metal material because contact resistance can bedecreased. It is also preferable to use a particle coated with layers oftwo or more kinds of metal materials, such as a particle coated withnickel and further with gold. As the connector 386, a material capableof elastic deformation or plastic deformation is preferably used. Asillustrated in FIG. 21, the conductive particle has a shape that isvertically crushed in some cases. With the crushed shape, the contactarea between the connector 386 and a conductive layer electricallyconnected to the connector 386 can be increased, thereby reducingcontact resistance and suppressing the generation of problems such asdisconnection.

The connector 386 is preferably provided so as to be covered with thebonding layer 317. For example, a paste or the like for forming thebonding layer 317 may be applied, and then, the connectors 386 may bescattered in the connection portion 385. A structure in which theconnection portion 385 is provided in a portion where the bonding layer317 is provided can be similarly applied not only to a structure inwhich the bonding layer 317 is also provided over the light-emittingelement 304 as illustrated in FIG. 21 (also referred to as a solidsealing structure) but also to, for example, a hollow sealing structurein which the bonding layer 317 is provided in the periphery of alight-emitting panel, a liquid crystal display panel, or the like.

FIG. 21 illustrates an example in which the optical adjustment layer 324does not cover an end portion of the electrode 321. In the example inFIG. 21, the spacer 316 is also provided in the driver circuit portion382.

Structure Example 10

In a touch panel illustrated in FIG. 22(A), the light-blocking layer 326is provided between the electrodes and the like in the touch sensor andthe flexible substrate 372. Specifically, the light-blocking layer 326is provided between the insulating layer 376 and an insulating layer328. Conductive layers including the electrodes 332 and 333 and thewirings 342, the insulating layer 395 covering these conductive layers,the electrode 334 over the insulating layer 395, and the like areprovided over the insulating layer 328. Furthermore, the insulatinglayer 327 is provided over the electrode 334 and the insulating layer395, and the coloring layer 325 is provided over the insulating layer327.

The insulating layers 327 and 328 have a function as a planarizationfilm. Note that the insulating layers 327 and 328 are not necessarilyprovided when not needed.

With such a structure, the light-blocking layer 326 provided in aposition closer to the flexible substrate 372 side than the electrodesand the like of the touch sensor can prevent the electrodes and the likefrom being seen by a user. Thus, a touch panel with not only a smallthickness but also improved display quality can be achieved.

As illustrated in FIG. 22(B), the touch panel may include alight-blocking layer 326 a between the insulating layer 376 and theinsulating layer 328 and may include a light-blocking layer 326 bbetween the insulating layer 327 and the bonding layer 317. Providingthe light-blocking layer 326 b can inhibit light leakage more surely.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 3 <Composition of CAC-OS>

Described below is the composition of a CAC (cloud alignedcomplementary)-OS applicable to a transistor disclosed in one embodimentof the present invention.

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in an active layer of a transistor iscalled an oxide semiconductor in some cases. In other words, an OS FETis a transistor including a metal oxide or an oxide semiconductor.

In this specification, a metal oxide in which regions functioning as aconductor and regions functioning as a dielectric are mixed and whichfunctions as a semiconductor as a whole is defined as a CAC (cloudaligned complementary)-OS (oxide semiconductor) or a CAC-metal oxide.

The CAC-OS has, for example, a composition in which elements included inan oxide semiconductor are unevenly distributed. Materials includingunevenly distributed elements each have a size of greater than or equalto 0.5 nm and less than or equal to 10 nm, preferably greater than orequal to 0.5 nm and less than or equal to 3 nm, or a similar size. Notethat in the following description of an oxide semiconductor, a state inwhich one or more elements are unevenly distributed and regionsincluding the element(s) are mixed is referred to as a mosaic pattern ora patch-like pattern. The region has a size of greater than or equal to0.5 nm and less than or equal to 10 nm, preferably greater than or equalto 0.5 nm and less than or equal to 3 nm, or a similar size.

The physical properties of a region including an unevenly distributedelement are determined by the properties of the element. For example, aregion including an unevenly distributed element which relatively tendsto serve as an insulator among elements included in a metal oxide servesas a dielectric region. In contrast, a region including an unevenlydistributed element which relatively tends to serve as a conductor amongelements included in a metal oxide serves as a conductive region. Amaterial in which conductive regions and dielectric regions are mixed toform a mosaic pattern serves as a semiconductor.

That is, a metal oxide in one embodiment of the present invention is akind of matrix composite or metal matrix composite, in which materialshaving different physical properties are mixed.

Note that an oxide semiconductor preferably contains at least indium. Inparticular, indium and zinc are preferably contained. In addition, anelement M (M is one or more of gallium, aluminum, silicon, boron,yttrium, copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like) may be contained.

For example, CAC-OS of an In—Ga—Zn oxide (an In—Ga—Zn oxide of CAC-OSmay be particularly referred to as CAC-IGZO) has a composition in whichmaterials are separated into indium oxide (InO_(X1), where X1 is a realnumber greater than 0) or indium zinc oxide (In_(X2)Zn_(Y2)O_(Z2), whereX2, Y2, and Z2 are real numbers greater than 0), and gallium oxide(GaO_(X3), where X3 is a real number greater than 0), gallium zinc oxide(Ga_(X4)Zn_(Y4)O_(Z4), where X4, Y4, and Z4 are real numbers greaterthan 0), or the like, and a mosaic pattern is formed. Then, InO_(X1) orIn_(X2)Zn_(Y2)O_(Z2) forming the mosaic pattern is evenly distributed inthe film. This composition is also referred to as a cloud-likecomposition.

That is, the CAC-OS is a composite oxide semiconductor with acomposition in which a region including GaO_(X3) as a main component anda region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main componentare mixed. Note that in this specification, for example, when the atomicratio of In to an element M in a first region is greater than the atomicratio of In to an element M in a second region, the first region hashigher In concentration than the second region.

Note that a compound including In, Ga, Zn, and O is also known as IGZO.Typical examples of IGZO include a crystalline compound represented byInGaO₃(ZnO)_(m1) (m1 is a natural number) and a crystalline compoundrepresented by In_((1+x0))Ga_((1−x0))O₃(ZnO)_(m0) (−1≤x0≤1; m0 is agiven number).

The above crystalline compounds have a single crystal structure, apolycrystalline structure, or a CAAC structure. Note that the CAACstructure is a crystal structure in which a plurality of IGZOnanocrystals have c-axis alignment and are connected in the a-b planedirection without alignment.

On the other hand, the CAC-OS relates to the material composition of anoxide semiconductor. In a material composition of a CAC-OS including In,Ga, Zn, and O, nanoparticle regions including Ga as a main component areobserved in part of the CAC-OS and nanoparticle regions including In asa main component are observed in part thereof. These nanoparticleregions are randomly dispersed to form a mosaic pattern. Therefore, thecrystal structure is a secondary element for the CAC-OS.

Note that in the CAC-OS, a stacked-layer structure including two or morefilms with different atomic ratios is not included. For example, atwo-layer structure of a film including In as a main component and afilm including Ga as a main component is not included.

A boundary between the region including GaO_(X3) as a main component andthe region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent is not clearly observed in some cases.

In the case where one or more of aluminum, silicon, boron, yttrium,copper, vanadium, beryllium, titanium, iron, nickel, germanium,zirconium, molybdenum, lanthanum, cerium, neodymium, hafnium, tantalum,tungsten, magnesium, and the like are contained instead of gallium in aCAC-OS, nanoparticle regions including the selected element(s) as a maincomponent(s) are observed in part of the CAC-OS and nanoparticle regionsincluding In as a main component are observed in part of the CAC-OS, andthese nanoparticle regions are randomly dispersed to form a mosaicpattern in the CAC-OS.

<Analysis of CAC-OS>

Next, measurement results of an oxide semiconductor over a substrate bya variety of methods are described.

<<Structure and Formation Method of Samples>>

Nine samples of one embodiment of the present invention are describedbelow. The samples are formed at different substrate temperatures andwith different ratios of an oxygen gas flow rate in formation of theoxide semiconductor. Note that each sample includes a substrate and anoxide semiconductor over the substrate.

A method for forming the samples is described.

A glass substrate is used as the substrate. Over the glass substrate, a100-nm-thick In—Ga—Zn oxide is formed as an oxide semiconductor with asputtering apparatus. The formation conditions are as follows: thepressure in a chamber is 0.6 Pa, and an oxide target (with an atomicratio of In:Ga:Zn=4:2:4.1) is used as a target. The oxide targetprovided in the sputtering apparatus is supplied with an AC power of2500 W.

As for the conditions in the formation of the oxide of the nine samples,the substrate temperature is set to a temperature that is not increasedby intentional heating (hereinafter such a temperature is also referredto as room temperature or R.T.), to 130° C., and to 170° C. The ratio ofa flow rate of an oxygen gas to a flow rate of a mixed gas of Ar andoxygen (also referred to as an oxygen gas flow rate ratio) is set to10%, 30%, and 100%.

<<Analysis by X-Ray Diffraction>>

In this section, results of X-ray diffraction (XRD) measurementperformed on the nine samples are described. As an XRD apparatus, D8ADVANCE manufactured by Bruker AXS is used. The conditions are asfollows: scanning is performed by an out-of-plane method at θ/2θ, thescanning range is 15 deg. to 50 deg., the step width is 0.02 deg., andthe scanning speed is 3.0 deg./min.

FIG. 34 shows XRD spectra measured by an out-of-plane method. In FIG.34, the top row shows the measurement results of the samples formed at asubstrate temperature of 170° C.; the middle row shows the measurementresults of the samples formed at a substrate temperature of 130° C.; thebottom row shows the measurement results of the samples formed at asubstrate temperature of R.T. The left column shows the measurementresults of the samples formed with an oxygen gas flow rate ratio of 10%;the middle column shows the measurement results of the samples formedwith an oxygen gas flow rate ratio of 30%; the right column shows themeasurement results of the samples formed with an oxygen gas flow rateratio of 100%.

In the XRD spectra shown in FIG. 34, the higher the substratetemperature at the time of formation is or the higher the oxygen gasflow rate ratio at the time of formation is, the higher the intensity ofthe peak at around 2θ=31° is. Note that it is found that the peak ataround 2θ=31° is derived from a crystalline IGZO compound whose c-axesare aligned in a direction substantially perpendicular to a formationsurface or a top surface of the crystalline IGZO compound (such acompound is also referred to as c-axis aligned crystalline (CAAC)-IGZO).

As shown in the XRD spectra in FIG. 34, as the substrate temperature atthe time of formation is lower or the oxygen gas flow rate ratio at thetime of formation is lower, a peak becomes less clear. Accordingly, itis found that there are no alignment in the a-b plane direction andc-axis alignment in the measured areas of the samples that are formed ata lower substrate temperature or with a lower oxygen gas flow rateratio.

<<Analysis with Electron Microscope>>

This section describes the observation and analysis results of thesamples formed at a substrate temperature of R.T. and with an oxygen gasflow rate ratio of 10% with a high-angle annular dark-field scanningtransmission electron microscope (HAADF-STEM). An image obtained with anHAADF-STEM is also referred to as a TEM image.

Described are the results of image analysis of plan-view images andcross-sectional images obtained with an HAADF-STEM (also referred to asplan-view TEM images and cross-sectional TEM images, respectively). TheTEM images are observed with a spherical aberration corrector function.The HAADF-STEM images are obtained using an atomic resolution analyticalelectron microscope JEM-ARM200F manufactured by JEOL Ltd. under thefollowing conditions: the acceleration voltage is 200 kV, andirradiation with an electron beam with a diameter of approximately 0.1nmφ is performed.

FIG. 35(A) is a plan-view TEM image of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10%. FIG.35(B) is a cross-sectional TEM image of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10%.

<<Analysis of Electron Diffraction Patterns>>

This section describes electron diffraction patterns obtained byirradiation of the sample formed at a substrate temperature of R.T. andan oxygen gas flow rate ratio of 10% with an electron beam with a probediameter of 1 nm (also referred to as a nanobeam).

Electron diffraction patterns of points indicated by a black dot a1, ablack dot a2, a black dot a3, a black dot a4, and a black dot a5 in theplan-view TEM image in FIG. 35(A) of the sample formed at a substratetemperature of R.T. and an oxygen gas flow rate ratio of 10% areobserved. Note that the electron diffraction patterns are observed whileelectron beam irradiation is performed at a constant rate for 35seconds. FIG. 35(C), FIG. 35(D), FIG. 35(E), FIG. 35(F), and FIG. 35(G)show the results of the points indicated by the black dot a1, the blackdot a2, the black dot a3, the black dot a4, and the black dot a5,respectively.

In FIG. 35(C), FIG. 35(D), FIG. 35(E), FIG. 35(F), and FIG. 35(G),regions with high luminance in a circular (ring) pattern can be shown.Furthermore, a plurality of spots can be shown in a ring-like shape.

Electron diffraction patterns of points indicated by a black dot b1, ablack dot b2, a black dot b3, a black dot b4, and a black dot b5 in thecross-sectional TEM image in FIG. 35(B) of the sample formed at asubstrate temperature of R.T. and an oxygen gas flow rate ratio of 10%are observed. FIG. 35(H), FIG. 35(I), FIG. 35(J), FIG. 35(K), and FIG.35(L) show the results of the points indicated by the black dot b1, theblack dot b2, the black dot b3, the black dot b4, and the black dot b5,respectively.

In FIG. 35(H), FIG. 35(I), FIG. 35(J), FIG. 35(K), and FIG. 35(L),regions with high luminance in a ring pattern can be shown. Furthermore,a plurality of spots can be shown in a ring-like shape.

For example, when an electron beam with a probe diameter of 300 nm isincident on a CAAC-OS including an InGaZnO₄ crystal in a directionparallel to the sample surface, a diffraction pattern including a spotderived from the (009) plane of the InGaZnO₄ crystal is obtained. Thatis, the CAAC-OS has c-axis alignment and the c-axes are aligned in thedirection substantially perpendicular to the formation surface or thetop surface of the CAAC-OS. Meanwhile, a ring-like diffraction patternis shown when an electron beam with a probe diameter of 300 nm isincident on the same sample in a direction perpendicular to the samplesurface. That is, it is found that the CAAC-OS has neither a-axisalignment nor b-axis alignment.

Furthermore, a diffraction pattern like a halo pattern is observed whenan oxide semiconductor including a nanocrystal (a nanocrystalline oxidesemiconductor (nc-OS)) is subjected to electron diffraction using anelectron beam with a large probe diameter (e.g., 50 nm or larger).Meanwhile, bright spots are shown in a nanobeam electron diffractionpattern of the nc-OS obtained using an electron beam with a small probediameter (e.g., smaller than 50 nm). Furthermore, in a nanobeam electrondiffraction pattern of the nc-OS, regions with high luminance in acircular (ring) pattern are shown in some cases. Also in a nanobeamelectron diffraction pattern of the nc-OS, a plurality of bright spotsare shown in a ring-like shape in some cases.

The electron diffraction pattern of the sample formed at a substratetemperature of R.T. and with an oxygen gas flow rate ratio of 10% hasregions with high luminance in a ring pattern and a plurality of brightspots appear in the ring-like pattern. Accordingly, the sample formed ata substrate temperature of R.T. and with an oxygen gas flow rate ratioof 10% exhibits an electron diffraction pattern similar to that of thenc-OS and does not show alignment in the plane direction and thecross-sectional direction.

According to what is described above, an oxide semiconductor formed at alow substrate temperature or with a low oxygen gas flow rate ratio islikely to have characteristics distinctly different from those of anoxide semiconductor film having an amorphous structure and an oxidesemiconductor film having a single crystal structure.

<<Elementary Analysis>>

This section describes the analysis results of elements included in thesample formed at a substrate temperature of R.T. and with an oxygen gasflow rate ratio of 10%. For the analysis, by energy dispersive X-rayspectroscopy (EDX), EDX mapping images are obtained. An energydispersive X-ray spectrometer AnalysisStation JED-2300T manufactured byJEOL Ltd. is used as an elementary analysis apparatus in the EDXmeasurement. A Si drift detector is used to detect an X-ray emitted fromthe sample.

In the EDX measurement, an EDX spectrum of a point is obtained in such amanner that electron beam irradiation is performed on the point in adetection target region of a sample, and the energy of characteristicX-ray of the sample generated by the irradiation and its frequency aremeasured. In this embodiment, peaks of an EDX spectrum of the point areattributed to electron transition to the L shell in an In atom, electrontransition to the K shell in a Ga atom, and electron transition to the Kshell in a Zn atom and the K shell in an O atom, and the proportions ofthe atoms in the point are calculated. An EDX mapping image indicatingdistributions of proportions of atoms can be obtained through theprocess in an analysis target region of a sample.

FIG. 36 shows EDX mapping images in a cross section of the sample formedat a substrate temperature of R.T. and with an oxygen gas flow rateratio of 10%. FIG. 36(A) shows an EDX mapping image of Ga atoms. Theproportion of the Ga atoms in all the atoms is 1.18 atomic % to 18.64atomic %. FIG. 36(B) shows an EDX mapping image of In atoms. Theproportion of the In atoms in all the atoms is 9.28 atomic % to 33.74atomic %. FIG. 36(C) shows an EDX mapping image of Zn atoms. Theproportion of the Zn atoms in all the atoms is 6.69 atomic % to 24.99atomic %. FIG. 36(A), FIG. 36(B), and FIG. 36(C) show the same region inthe cross section of the sample formed at a substrate temperature ofR.T. and with an oxygen gas flow rate ratio of 10%. In the EDX mappingimages, the proportion of an element is indicated by grayscale: the moremeasured atoms exist in a region, the brighter the region is; the lessmeasured atoms exist in a region, the darker the region is. Themagnification of the EDX mapping images in FIG. 36 is 7200000 times.

The EDX mapping images in FIG. 36(A), FIG. 36(B), and FIG. 36(C) showrelative distribution of brightness indicating that each element has adistribution in the sample formed at a substrate temperature of R.T. andwith an oxygen gas flow rate ratio of 10%. Areas surrounded by solidlines and areas surrounded by dashed lines in FIG. 36(A), FIG. 36(B),and FIG. 36(C) are examined.

In FIG. 36(A), a relatively dark region occupies a large area in thearea surrounded by the solid line, while a relatively bright regionoccupies a large area in the area surrounded by the dashed line. In FIG.36(B), a relatively bright region occupies a large area in the areasurrounded by the solid line, while a relatively dark region occupies alarge area in the area surrounded by the dashed line.

That is, the areas surrounded by the solid lines are regions including arelatively large number of In atoms and the areas surrounded by thedashed lines are regions including a relatively small number of Inatoms. In FIG. 36(C), the right portion of the area surrounded by thesolid line is relatively bright and the left portion thereof isrelatively dark. Thus, the area surrounded by the solid line is a regionincluding In_(X2)Zn_(Y2)O_(Z2), InO_(X1), or the like as a maincomponent.

The area surrounded by the solid line is a region including a relativelysmall number of Ga atoms and the area surrounded by the dashed line is aregion including a relatively large number of Ga atoms. In FIG. 36(C),the upper left portion of the area surrounded by the dashed line isrelatively bright and the lower right portion thereof is relativelydark. Thus, the area surrounded by the dashed line is a region includingGaO_(X3), Ga_(X4)Zn_(Y4)O_(Z4), or the like as a main component.

Furthermore, as shown in FIG. 36(A), FIG. 36(B), and FIG. 36(C), the Inatoms are relatively more uniformly distributed than the Ga atoms, andregions including InO_(X1) as a main component are seemingly joined toeach other through a region including In_(X2)Zn_(Y2)O_(Z2) as a maincomponent. Thus, the regions including In_(X2)Zn_(Y2)O_(Z2) and InO_(X1)as main components extend like a cloud.

An In—Ga—Zn oxide having a composition in which the regions includingGaO_(X3) or the like as a main component and the regions includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component are unevenlydistributed and mixed can be referred to as a CAC-OS.

The crystal structure of the CAC-OS includes an nc structure. In anelectron diffraction pattern of the CAC-OS with the nc structure,several or more bright spots appear in addition to bright sports derivedfrom IGZO including a single crystal, a polycrystal, or a CAAC.Alternatively, the crystal structure is defined as having high luminanceregions appearing in a ring pattern in addition to the several or morebright spots.

As shown in FIG. 36(A), FIG. 36(B), and FIG. 36(C), each of the regionsincluding GaO_(X3) or the like as a main component and the regionsincluding In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component has asize of greater than or equal to 0.5 nm and less than or equal to 10 nm,or greater than or equal to 1 nm and less than or equal to 3 nm. Notethat it is preferable that a diameter of a region including each metalelement as a main component be greater than or equal to 1 nm and lessthan or equal to 2 nm in the EDX mapping images.

As described above, the CAC-OS has a structure different from that of anIGZO compound in which metal elements are evenly distributed, and hascharacteristics different from those of the IGZO compound. That is, inthe CAC-OS, regions including GaO_(X3) or the like as a main componentand regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent are separated to form a mosaic pattern.

The conductivity of a region including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1)as a main component is higher than that of a region including GaO_(X3)or the like as a main component. In other words, when carriers flowthrough regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a maincomponent, the conductivity of an oxide semiconductor is exhibited.Accordingly, when regions including In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) asa main component are distributed in an oxide semiconductor like a cloud,high field-effect mobility (μ) can be achieved.

In contrast, the insulating property of a region including GaO_(X3) orthe like as a main component is higher than that of a region includingIn_(X2)Zn_(Y2)O_(Z2) or InO_(X1) as a main component. In other words,when regions including GaO_(X3) or the like as a main component aredistributed in an oxide semiconductor, leakage current can be suppressedand favorable switching operation can be achieved.

Accordingly, when a CAC-OS is used for a semiconductor element, theinsulating property derived from GaO_(X3) or the like and theconductivity derived from In_(X2)Zn_(Y2)O_(Z2) or InO_(X1) complementeach other, whereby high on-state current (I_(on)) and high field-effectmobility (μ) can be achieved.

A semiconductor element including a CAC-OS has high reliability. Thus,the CAC-OS is suitably used in a variety of semiconductor devicestypified by a display.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 4

In this embodiment, electronic devices and lighting devices ofembodiments of the present invention will be described with reference todrawings.

Electronic devices with reduced display defects can be obtained usingthe display device of one embodiment of the present invention.Electronic devices having a curved surface or flexibility can beobtained using the display device of one embodiment of the presentinvention. Thin or lightweight electronic devices can be obtained usingthe display device of one embodiment of the present invention.

Examples of electronic devices are a television set, wearable displayssuch as a wristband display and a goggle-type display (head mounteddisplay), a monitor of a computer or the like, cameras such as a digitalcamera and a digital video camera, a digital photo frame, a mobilephone, a portable game machine, a portable information terminal, anaudio reproducing device, and a large-sized game machine such as apachinko machine.

The electronic device of one embodiment of the present invention hasflexibility and therefore can be incorporated along a curvedinside/outside wall surface of a house or a building or a curvedinterior/exterior surface of a car.

Furthermore, the electronic device of one embodiment of the presentinvention may include a secondary battery. It is preferable that thesecondary battery be capable of being charged by non-contact powertransmission.

Examples of the secondary battery include a lithium ion secondarybattery such as a lithium polymer battery using a gel electrolyte(lithium ion polymer battery), a nickel-hydride battery, anickel-cadmium battery, an organic radical battery, a lead-acid battery,an air secondary battery, a nickel-zinc battery, and a silver-zincbattery.

The electronic device of one embodiment of the present invention mayinclude an antenna. When a signal is received by the antenna, theelectronic device can display an image, data, or the like on a displayportion. When the electronic device includes a secondary battery, theantenna may be used for contactless power transmission.

FIGS. 23(A) to (E) show examples of electronic devices each including adisplay portion 7001 having flexibility.

The display portion 7001 is manufactured using the display device of oneembodiment of the present invention. For example, a display device thatcan be bent with a radius of curvature of greater than or equal to 0.01mm and less than or equal to 150 mm can be used. The display portion7001 may include a touch sensor so that the electronic device can beoperated by touching the display portion 7001 with a finger or the like.

One embodiment of the present invention makes it possible to provide anelectronic device with reduced display defects which includes a displayportion having flexibility.

FIGS. 23(A) to (C) illustrate an example of a foldable electronicdevice. FIG. 23(A) illustrates an electronic device 7600 that is opened.FIG. 23(B) illustrates the electronic device 7600 that is being openedor being folded. FIG. 23(C) illustrates the electronic device 7600 thatis folded. The electronic device 7600 is highly portable when folded,and is highly browsable when opened because of a seamless large displayarea.

A display portion 7001 is supported by three housings 7601 joinedtogether by hinges 7602. By folding the electronic device 7600 at aconnection portion between two housings 7601 with the hinges 7602, theelectronic device 7600 can be reversibly changed in shape from an openedstate to a folded state.

FIGS. 23(D) and (E) illustrate an example of a foldable electronicdevice. FIG. 23(D) illustrates an electronic device 7650 that is foldedinward and FIG. 23(E) illustrates the electronic device 7650 that isfolded outward. The electronic device 7650 includes the display portion7001 and a non-display portion 7651. When the electronic device 7650 isnot used, the electronic device 7650 is folded so that the displayportion 7001 is on the inside, whereby the display portion 7001 can beprevented from being contaminated or damaged.

The electronic device 7600 and the electronic device 7650 can each beused as a portable information terminal. Each of the portableinformation terminals illustrated in this embodiment functions as, forexample, one or more of a telephone set, a notebook, and an informationbrowsing system. Specifically, each of the portable informationterminals can be used as a smartphone. The portable information terminalis capable of executing a variety of applications such as mobile phonecalls, e-mailing, reading and editing texts, music reproduction,Internet communication, and a computer game.

Foldable electronic devices are described in detail with reference toFIG. 24 to FIG. 27. FIG. 24 to FIG. 27 show examples where the touchpanel 300 (see FIG. 14 and FIG. 15) is used as a display panel.

Electronic devices illustrated in FIG. 24 to FIG. 27 include astrip-like high flexibility region and a strip-like low flexibilityregion that are arranged alternately. These electronic devices can befolded by bending the high flexibility region. These electronic devicesare highly portable in a folded state, and are highly browsable in anopened state because of a seamless large light-emitting region. The highflexibility region can be bent either inward or outward.

When the electronic device is in use, it can be opened so that theseamless large display region is entirely used, or it can be folded suchthat the display surface of the display panel faces outward and thedisplay region can be partly used. When the display region that isfolded and hidden from a user is a non-display region, the powerconsumption of the electronic device can be reduced.

FIGS. 24(A) to 24(D) illustrate an electronic device 90 that can befolded in three parts and includes two strip-like high flexibilityregions and three strip-like low flexibility regions. FIGS. 24(A) and(C) are plan views of the display surface side of the electronic device90, and FIGS. 24(B) and (D) are plan views of the side opposite to thedisplay surface of the electronic device 90.

Note that the number of high flexibility regions and the number of lowflexibility regions are not particularly limited. FIG. 25(A) illustratesan electronic device that can be folded in two parts and includes onestrip-like high flexibility region and two strip-like low flexibilityregions. FIG. 25(B) illustrates an electronic device that includes threestrip-like high flexibility regions and four strip-like low flexibilityregions. FIG. 25(C) illustrates an electronic device that includes fourstrip-like high flexibility regions and five strip-like low flexibilityregions.

The electronic device 90 illustrated in FIGS. 24(A) to (D) includes thetouch panel 300 having flexibility, a protective layer 93, theconductive layer 73, a plurality of support panels 95 a, and a pluralityof support panels 95 b. Each of the support panels 95 a and 95 b has alower flexibility than the touch panel 300. The plurality of supportpanels 95 a are apart from each other. The plurality of support panels95 b are apart from each other.

As illustrated in FIG. 24(A), the electronic device 90 includes highflexibility regions E1 and low flexibility regions E2 that are arrangedalternately in one direction. The high flexibility region and the lowflexibility region are strip-like regions (form stripes). In thisembodiment, a plurality of high flexibility regions and a plurality oflow flexibility regions are parallel to each other; however, the regionsare not necessarily arranged parallel to each other.

The high flexibility region E1 in the electronic device 90 includes atleast a flexible display panel. In particular, a display panel usingorganic EL elements is particularly preferable because it not only hashigh flexibility and impact resistance but also can be thinned andlightened.

The low flexibility region E2 in the electronic device 90 includes atleast a flexible display panel and a support panel having a lowerflexibility than that of the display panel and overlapping with thedisplay panel.

FIG. 26(A) illustrates the state where the electronic device 90illustrated in FIG. 24(A) is opened. FIG. 26(B) illustrates theelectronic device 90 that is being opened or being folded. FIG. 26(C)illustrates the electronic device 90 that is folded.

FIG. 27 is a perspective view illustrating components of the electronicdevice 90 illustrated in FIG. 24(A).

Here, when an end portion (also referred to as a folded portion or thelike) of the touch panel 300 is located outward from end portions of thesupport panels 95 a and 95 b in the electronic device 90 in a foldedstate, the touch panel 300 is damaged or an element included in thetouch panel 300 is broken in some cases.

In the electronic device 90 in a folded state shown in FIG. 26(C), theend portion of the touch panel 300 is aligned with the end portions ofthe support panels 95 a and 95 b positioned over and below the touchpanel 300. This structure can prevent damage to the touch panel 300,breakage of an element included in the touch panel 300, and the like.

Moreover, when the electronic device 90 illustrated in FIG. 24(C) isfolded, the end portion of the touch panel 300 is positioned inward fromthe end portions of the support panels 95 a and 95 b. This structure canfurther prevent damage to the touch panel 300, breakage of an elementincluded in the touch panel 300, and the like.

In FIG. 24(C), a length W1 to a length W3 represent the lengths of thelow flexibility regions in the direction in which the high flexibilityregion and the low flexibility region are arranged.

The low flexibility region preferably includes an external connectionelectrode of the display panel. Here, the external connection electrodecorresponds to, for example, the conductive layer 355 in FIG. 15.

In FIG. 24(C), the low flexibility region with the length W1 includesthe external connection electrode. In the electronic device 90, thelength W1 of a low flexibility region A overlapping with the externalconnection electrode is longer than the length W3 of a low flexibilityregion B that is closer to the region A.

In the electronic device 90, it is preferable that the length W1 of thelow flexibility region A overlapping with the external connectionelectrode be longer than the length W3 of the low flexibility region Bthat is closer to the region A. It is particularly preferable that,among the length W1 of the region A, the length W3 of the region B, andthe length W2 of a low flexibility region C that is farther from theregion A, W1 be the longest and W2 be the second longest.

Similarly, in the electronic device illustrated in FIG. 25(B), thelength W1 is the longest, the length W2 is the second longest, and thelength W3 and the length W4 are the shortest among the length W1 to thelength W4. The length W3 and the length W4 may be different lengths.

In addition, in the electronic device illustrated in FIG. 25(C), thelength W1 is the longest, the length W2 is the second longest, and thelength W3, the length W4, and the length W5 are the shortest among thelength W1 to the length W5. The length W3, the length W4, and the lengthW5 may be different lengths.

The support panel is provided on at least one of the display surfaceside and the side opposite to the display surface side of the displaypanel.

The display panel preferably has support panels on both the displaysurface side and the side opposite to the display surface side, like thesupport panels 95 a and 95 b, in which case the display panel can besandwiched between a pair of support panels; thus, the mechanicalstrength of the low flexibility region is increased and the electronicdevice 90 becomes less likely to be broken.

The high flexibility region E1 and the low flexibility region E2preferably include the display panel and a protective layer having ahigher flexibility than that of the support panel and overlapping withthe display panel. In that case, the high flexibility region E1 in theelectronic device 90 can have high mechanical strength as well asflexibility and the electronic device 90 becomes less likely to bebroken. This structure makes the electronic device 90 less likely to bebroken by deformation due to external force or the like in the highflexibility region as well as the low flexibility region.

For example, it is preferable that the support panel be the thickest andthe display panel be the thinnest among the display panel, the supportpanel, and the protective layer. Alternatively, for example, it ispreferable that the support panel have the lowest flexibility and thedisplay panel have the highest flexibility among the display panel, thesupport panel, and the protective layer. Such a structure increases thedifference in flexibility between the high flexibility region and thelow flexibility region. Thus, the electronic device can be foldedreliably at the high flexibility region, so that the low flexibilityregion is prevented from being bent. Consequently, the reliability ofthe light-emitting device can be improved. Such a structure alsoprevents the electronic device from being bent at an undesired portion.

The display panel preferably has protective layers on both the displaysurface side and the side opposite to the display surface side, in whichcase the display panel can be sandwiched between a pair of protectivelayers; thus, the electronic device has increased mechanical strengthand the electronic device becomes less likely to be broken.

In this embodiment, an example where the conductive layer 73 functionsas a protective layer is shown. The conductive layer 73 is connected tothe support panel 95 b or a battery and thus is supplied with a constantpotential.

For example, as illustrated in FIG. 24(A), FIG. 27, and the like, in thelow flexibility region E2, it is preferable that the protective layer 93and the conductive layer 73 be placed between the pair of support panels95 a and 95 b and the touch panel 300 be placed between the protectivelayer 93 and the conductive layer 73.

It is preferable that the display panel have the protective layer ononly one of the display surface side and the side opposite to thedisplay surface side because the electronic device 90 can be thinner ormore lightweight. For example, the electronic device 90 that includesthe conductive layer 73 and does not include the protective layer 93 maybe employed.

When the protective layer 93 on the display surface side of the displaypanel is a light-blocking film, a non-display region of the displaypanel can be prevented from being irradiated with external light. Thisstructure is preferable because it prevents photodegradation of atransistor and the like of a driver circuit that is included in thenon-display region.

The touch panel 300 includes a portion not fixed to the conductive layer73, whereby, when the electronic device 90 is bent or opened, theposition of at least one portion of the touch panel 300 relative to theconductive layer 73 is changed. In addition, a neutral plane can beformed in the touch panel 300; thus, the touch panel 300 can beprevented from being broken due to power applied to the touch panel 300.

The protective layer and the support panel can be formed using plastic,a metal, an alloy, rubber, or the like. Plastic, rubber, or the like ispreferably used because it can form a protective layer or a supportpanel that is lightweight and less likely to be broken. For example,silicone rubber can be used for the protective layer 93, a conductivefilm can be used for the conductive layer 73, and stainless steel oraluminum can be used for the support panel. As the conductive film, forexample, a film in which ITO and a PET film are stacked can be used.

The protective layer and the support panel are preferably formed using amaterial with high toughness. In that case, an electronic device withhigh impact resistance that is less likely to be broken can be provided.For example, when a resin, a thin metal material, or a thin alloymaterial is used for the protective layer and the support panel, theelectronic device can be lightweight and less likely to be broken. For asimilar reason, also a substrate of the display panel is preferablyformed using a material with high toughness.

The protective layer and the support panel on the display surface sidedo not necessarily have a light-transmitting property if they do notoverlap with the display region of the display panel. When theprotective layer and the support panel on the display surface sideoverlap with at least part of the display region, they are preferablyformed using a material that transmits light emitted from thelight-emitting element. There is no limitation on the light-transmittingproperty of the protective layer and the support panel on the sideopposite to the display surface side.

When any two of the protective layer, the support panel, and the displaypanel are bonded to each other, any of a variety of adhesives can beused, and for example, resins such as a curable resin that is curable atroom temperature (e.g., a two-component-mixture-type resin), a lightcurable resin, and a thermosetting resin can be used. Alternatively, asheet-like adhesive may be used. Alternatively, components of theelectronic device may be fixed with, for example, a screw thatpenetrates two or more of the protective layer, the support panel, andthe display panel, a pin or clip that holds them, or the like. The touchpanel 300 includes a portion not fixed to the conductive layer 73.

The electronic device 90 can be used with one display panel (one displayregion) divided into two or more regions at a folded portion(s). Forexample, it is possible to put the region that is hidden by folding thelight-emitting device in a non-display state and put only the exposedregion in a display state. Thus, power consumed by a region that is notused by a user can be reduced.

The electronic device 90 may include a sensor for determining whethereach high flexibility region is bent or not. The sensor can be composedof, for example, a switch, a MEMS pressure sensor, a pressure sensor, orthe like.

In the electronic device 90, one display panel can be folded once ormore times. The curvature radius in that case can be, for example,greater than or equal to 1 mm and less than or equal to 150 mm.

FIGS. 28(A) to (D) show examples of an arm-worn electronic device and awatch-type electronic device. In FIG. 28, examples where the touch panel300 (see FIG. 14 and FIG. 15) is used as a display panel are shown.

Usage of electronic devices of one embodiment of the present inventionis not particularly limited. For example, the electronic devices may beused without being worn on or may be used while being worn on part of abody such as an arm, a waist, or a leg or being attached to a robot(e.g., a factory robot and a humanoid robot), a columnar object (e.g., acolumn of a building, a utility pole, and an indicator pole), a tool, orthe like.

FIG. 28(A) illustrates a top view of an arm-worn electronic device 60and FIG. 28(B) illustrates a cross-sectional view taken alongdashed-dotted line X-Y in FIG. 28(A). In FIG. 28(B), a direction inwhich light emitted from the light-emitting element included in thetouch panel 300 is denoted by arrows.

The electronic device 60 includes a housing 61 and a band 65. Inside thehousing 61, the touch panel 300, the conductive layer 73, a circuit, apower storage device 67, and the like are provided. The housing 61 isconnected to the band 65. The housing 61 and the band 65 may beconnected to each other detachably.

The touch panel 300 includes the conductive layer 390 illustrated inFIG. 15. The conductive layer 390 is electrically connected to theconductive layer 73 and is supplied with a constant potential. Theconductive layer 73 is supplied with a constant potential. Theconductive layer 73 may be connected to the power storage device 67 orthe housing 61. For example, the conductive layer 73 is electricallyconnected to the GND line of the housing 61 or the battery, and issupplied with the GND potential.

The conductive layer 73 may function as a shield for electrostaticshielding of the power storage device 67. In particular, the conductivelayer 73 is preferable as a shield of a secondary battery which does notneed an exterior body (e.g., solid-state battery). Furthermore, theconductive layer 73 may function as a shield for electrostatic shieldingof a variety of sensors included in the electronic device 60.

As the band, a belt-like band or a chain-like band can be used.

FIG. 28(C) shows an example including a chain-like band 68. FIG. 28(C)illustrates an arm-worn electronic device including a circular displayregion 81 in a circular housing 61.

For the band which enables the electronic device to be worn on the armor the like, one or more of a metal, a resin, a natural material, andthe like can be used. As the metal, stainless steel, aluminum, atitanium alloy, or the like can be used. As the resin, an acrylic resin,a polyimide resin, or the like can be used. As the natural material,processed wood, stone, bone, leather, paper, or cloth can be used, forexample.

FIG. 28(D) illustrates an example of a wrist-watch-type electronicdevice. An electronic device 7800 includes a band 7801, the displayportion 7001, an input/output terminal 7802, operation buttons 7803, andthe like. The band 7801 has a function as a housing. A flexible battery7805 can be included in the electronic device 7800. The battery 7805 maybe provided to overlap with the display portion 7001 or the band 7801,for example.

The band 7801, the display portion 7001, and the battery 7805 haveflexibility. Thus, the electronic device 7800 can be easily curved tohave a desired shape.

The electronic device 7800 can be used as a portable informationterminal.

With the operation buttons 7803, a variety of functions such as timesetting, ON/OFF of the power, ON/OFF of wireless communication, settingand cancellation of silent mode, and setting and cancellation of powersaving mode can be performed. For example, the functions of theoperation buttons 7803 can be set freely by the operating systemincorporated in the electronic device 7800.

By touch on an icon 7804 displayed on the display portion 7001 with afinger or the like, application can be started.

The electronic device 7800 can employ near field communication that is acommunication method based on an existing communication standard. Inthat case, for example, mutual communication between the electronicdevice 7800 and a headset capable of wireless communication can beperformed, and thus hands-free calling is possible.

The electronic device 7800 may include the input/output terminal 7802.In the case where the input/output terminal 7802 is included in theelectronic device 7800, data can be directly transmitted to and receivedfrom another information terminal via a connector. Charging through theinput/output terminal 7802 is also possible. Note that charging may beperformed by contactless power transmission without using theinput/output terminal.

FIGS. 29(A), (B), (C1), (C2), (D), and (E) illustrate examples ofelectronic devices each including a display portion 7000 with a curvedsurface. The display surface of the display portion 7000 is curved, andimages can be displayed on the curved display surface. Note that thedisplay portion 7000 may be flexible.

The display portion 7000 can be formed using the display device of oneembodiment of the present invention.

One embodiment of the present invention makes it possible to provide anelectronic device with reduced display defects and having a curveddisplay portion.

FIG. 29(A) illustrates an example of a mobile phone. A mobile phone 7100includes a housing 7101, the display portion 7000, operation buttons7103, an external connection port 7104, a speaker 7105, a microphone7106, and the like.

The mobile phone 7100 illustrated in FIG. 29(A) includes a touch sensorin the display portion 7000. Operations such as making a call andinputting a letter can be performed by touch on the display portion 7000with a finger, a stylus, or the like.

With the operation buttons 7103, power ON or OFF can be switched. Inaddition, types of images displayed on the display portion 7000 can beswitched; for example, switching images from a mail creation screen to amain menu screen is performed with the operation button 7103.

FIG. 29(B) illustrates an example of a television set. In a televisionset 7200, the display portion 7000 is incorporated in a housing 7201.Here, the housing 7201 is supported by a stand 7203.

The television set 7200 illustrated in FIG. 29(B) can be operated withan operation switch of the housing 7201 or a separate remote controller7211. The display portion 7000 may include a touch sensor, and can beoperated by touch on the display portion 7000 with a finger or the like.The remote controller 7211 may be provided with a display portion fordisplaying data output from the remote controller 7211. With operationkeys or a touch panel of the remote controller 7211, channels and volumecan be controlled and images displayed on the display portion 7000 canbe controlled.

Note that the television set 7200 is provided with a receiver, a modem,or the like. A general television broadcast can be received with thereceiver. When the television set is connected to a communicationnetwork with or without wires via the modem, one-way (from a transmitterto a receiver) or two-way (between a transmitter and a receiver orbetween receivers) data communication can be performed.

FIGS. 29(C1), (C2), (D), and (E) illustrate examples of portableinformation terminals. Each of the portable information terminalsincludes a housing 7301 and the display portion 7000. Each of theportable information terminals may also include an operation button, anexternal connection port, a speaker, a microphone, an antenna, abattery, or the like. The display portion 7000 is provided with a touchsensor. An operation of the portable information terminal can beperformed by touch on the display portion 7000 with a finger, a stylus,or the like.

FIG. 29(C1) is a perspective view of a portable information terminal7300. FIG. 29(C2) is a top view of the portable information terminal7300. FIG. 29(D) is a perspective view of a portable informationterminal 7310. FIG. 29(E) is a perspective view of a portableinformation terminal 7320.

The portable information terminals 7300, 7310, and 7320 can each displaycharacters and image information on its plurality of surfaces. Forexample, as illustrated in FIGS. 29(C1) and (D), three operation buttons7302 can be displayed on one surface, and information 7303 indicated bya rectangle can be displayed on another surface. FIGS. 29(C1) and (C2)illustrate an example in which information is displayed on the topsurface of the portable information terminal. FIG. 29(D) illustrates anexample in which information is displayed on the side surface of theportable information terminal. Information may be displayed on three ormore surfaces of the portable information terminal. FIG. 29(E)illustrates an example in which information 7304, information 7305, andinformation 7306 are displayed on different surfaces.

Examples of the information include notification from a socialnetworking service (SNS), display indicating reception of an e-mail oran incoming call, the title of an e-mail or the like, the sender of ane-mail or the like, the date, the time, remaining battery, and thereception strength of an antenna. Alternatively, the operation button,an icon, or the like may be displayed instead of the information.

For example, a user of the portable information terminal 7300 can seethe display (here, the information 7303) with the portable informationterminal 7300 put in a breast pocket of his/her clothes.

Specifically, a caller's phone number, name, or the like of an incomingcall is displayed in the position that can be seen from above theportable information terminal 7300. Thus, the user can see the displaywithout taking out the portable information terminal 7300 from thepocket and decide whether to answer the call.

FIGS. 29(F) to (H) each illustrate an example of a lighting devicehaving a curved light-emitting portion.

The light-emitting portion included in each of the lighting devicesillustrated in FIGS. 29(F) to (H) can be formed using the display deviceof one embodiment of the present invention.

One embodiment of the present invention makes it possible to provide alighting device with reduced light-emission defects and having a curvedlight-emitting portion.

A lighting device 7400 illustrated in FIG. 29(F) includes alight-emitting portion 7402 with a wave-shaped light-emitting surfaceand thus is a good-design lighting device.

A light-emitting portion 7412 included in a lighting device 7410illustrated in FIG. 29(G) has two convex-curved light-emitting portionssymmetrically placed. Thus, all directions can be illuminated with thelighting device 7410 as a center.

A lighting device 7420 illustrated in FIG. 29(H) includes aconcave-curved light-emitting portion 7422. This is suitable forilluminating a specific range because light emitted from thelight-emitting portion 7422 is collected to the front of the lightingdevice 7420.

The light-emitting portion included in each of the lighting devices7400, 7410, and 7420 may be flexible. The light-emitting portion may befixed on a plastic member, a movable frame, or the like so that alight-emitting surface of the light-emitting portion can be bent freelydepending on the intended use.

The lighting devices 7400, 7410, and 7420 each include a stage 7401provided with an operation switch 7403 and a light-emitting portionsupported by the stage 7401.

Note that although the lighting device in which the light-emittingportion is supported by the stage is described as an example here, ahousing provided with a light-emitting portion can be fixed on a ceilingor suspended from a ceiling. Since the light-emitting surface can becurved, the light-emitting surface is curved to have a concave shape,whereby a particular area can be brightly illuminated, or thelight-emitting surface is curved to have a convex shape, whereby a wholeroom can be brightly illuminated.

With the flexible display device of one embodiment of the presentinvention, an electronic device having a structure other than the foldeddisplay portion (e.g., FIG. 23) can be manufactured.

FIGS. 30(A) to (D) each illustrate an example of a portable informationterminal including a display portion 7001 having flexibility.

FIG. 30(A) is a perspective view illustrating an example of the portableinformation terminal and FIG. 30(B) is a side view illustrating theexample of the portable information terminal. A portable informationterminal 7500 includes a housing 7501, the display portion 7001, adisplay portion tab 7502, operation buttons 7503, and the like.

The portable information terminal 7500 includes a rolled flexibledisplay portion 7001 in the housing 7501.

The portable information terminal 7500 can receive a video signal with acontrol portion incorporated therein and can display the received videoon the display portion 7001. The portable information terminal 7500incorporates a battery. A terminal portion for connecting a connectormay be included in the housing 7501 so that a video signal and power canbe directly supplied from the outside with a wiring.

By pressing the operation buttons 7503, power ON/OFF, switching ofdisplayed videos, and the like can be performed. Although FIGS. 30(A) to(C) illustrate an example in which the operation buttons 7503 arepositioned on a side surface of the portable information terminal 7500,one embodiment of the present invention is not limited thereto. Theoperation buttons 7503 may be placed on a display surface (a frontsurface) or a rear surface of the portable information terminal 7500.

FIG. 30(C) illustrates the portable information terminal 7500 in a statewhere the display portion 7001 is pulled out. Images can be displayed onthe display portion 7001 in this state. In addition, the portableinformation terminal 7500 may perform different displays in the statewhere part of the display portion 7001 is rolled as illustrated in FIG.30(A) and in the state where the display portion 7001 is pulled out bythe display portion tab 7502 as illustrated in FIG. 30(C). For example,in the state illustrated in FIG. 30(A), the rolled portion of thedisplay portion 7001 is put in a non-display state, which results in areduction in power consumption of the portable information terminal7500.

Note that a reinforcement frame may be provided for a side portion ofthe display portion 7001 so that the display portion 7001 has a flatdisplay surface when pulled out.

Note that in addition to this structure, a speaker may be provided forthe housing so that sound is output with an audio signal receivedtogether with a video signal.

FIG. 30(D) illustrates an example of a flexible portable informationterminal. A portable information terminal 7700 includes a housing 7701and the display portion 7001. The portable information terminal 7700 mayfurther include buttons 7703 a and 7703 b which serve as input means,speakers 7704 a and 7704 b which serve as sound output means, anexternal connection port 7705, a microphone 7706, or the like. Aflexible battery 7709 can be included in the portable informationterminal 7700. The battery 7709 may be provided to overlap with thedisplay portion 7001, for example.

The housing 7701, the display portion 7001, and the battery 7709 areflexible. Thus, it is easy to curve the portable information terminal7700 into a desired shape and to twist the portable information terminal7700. For example, the portable information terminal 7700 can be foldedso that the display portion 7001 is on the inside or on the outside. Theportable information terminal 7700 can be used in a rolled state. Sincethe housing 7701 and the display portion 7001 can be transformed freelyin this manner, the portable information terminal 7700 is less likely tobe broken even when the portable information terminal 7700 falls down orexternal stress is applied to the portable information terminal 7700.

The portable information terminal 7700 is lightweight and therefore canbe used conveniently in various situations. For example, the portableinformation terminal 7700 can be used in the state where the upperportion of the housing 7701 is suspended by a clip or the like, or inthe state where the housing 7701 is fixed to a wall by magnets or thelike.

FIG. 31(A) illustrates an external view of an automobile 9700. FIG.31(B) illustrates a driver's seat of the automobile 9700. The automobile9700 includes a car body 9701, wheels 9702, a dashboard 9703, lights9704, and the like. The display device of one embodiment of the presentinvention can be used in a display portion or the like of the automobile9700. For example, the display device of one embodiment of the presentinvention can be provided in a display portion 9710 to a display portion9715 illustrated in FIG. 31(B).

The display portion 9710 and the display portion 9711 are displaydevices provided in an automobile windshield. The display device of oneembodiment of the present invention can be a see-through device, throughwhich the opposite side can be seen, by using a light-transmittingconductive material for its electrodes and wirings. Such a see-throughdisplay portion 9710 or 9711 does not hinder driver's vision duringdriving of the automobile 9700. Thus, the display device of oneembodiment of the present invention can be provided in the windshield ofthe automobile 9700. Note that in the case where a transistor or thelike for driving the display device or the like is provided, atransistor having light-transmitting properties, such as an organictransistor using an organic semiconductor material or a transistor usingan oxide semiconductor, is preferably used.

The display portion 9712 is a display device provided on a pillarportion. For example, the display portion 9712 can compensate for theview hindered by the pillar portion by showing an image taken by animaging unit provided on the car body. The display portion 9713 is adisplay device provided on the dashboard. For example, the displayportion 9713 can compensate for the view hindered by the dashboardportion by showing an image taken by an imaging unit provided on the carbody. That is, showing an image taken by an imaging unit provided on theoutside of the car body leads to elimination of blind areas andenhancement of safety. In addition, showing an image so as to compensatefor the area which a driver cannot see makes it possible for the driverto confirm safety easily and comfortably.

FIG. 31(C) illustrates the inside of an automobile in which a bench seatis used as a driver seat and a front passenger seat. A display portion9721 is a display device provided in a door portion. For example, thedisplay portion 9721 can compensate for the view hindered by the doorportion by showing an image taken by an imaging unit provided on the carbody. A display portion 9722 is a display device provided in a steeringwheel. A display portion 9723 is a display device provided in the middleof a seating face of the bench seat. Note that the display device can beused as a seat heater by providing the display device on the seatingface or backrest and by using heat generated by the display device as aheat source.

The display portion 9714, the display portion 9715, and the displayportion 9722 can provide a variety of kinds of information such asnavigation data, a speedometer, a tachometer, a mileage, a fuel meter, agearshift indicator, and air-condition setting. The content, layout, orthe like of the display on the display portions can be changed freely bya user as appropriate. The information listed above can also bedisplayed on the display portions 9710 to 9713, 9721, and 9723. Thedisplay portions 9710 to 9715 and 9721 to 9723 can also be used aslighting devices. The display portions 9710 to 9715 and 9721 to 9723 canalso be used as heating devices.

A display portion including the display device of one embodiment of thepresent invention may be flat. In this case, the display device of oneembodiment of the present invention does not necessarily have a curvedsurface or flexibility. When the display device of one embodiment of thepresent invention is used, a thin and lightweight electronic device ispossible.

FIG. 31(D) illustrates a portable game console including a housing 9801,a housing 9802, a display portion 9803, a display portion 9804, amicrophone 9805, a speaker 9806, an operation key 9807, a stylus 9808,and the like.

The portable game console illustrated in FIG. 31(D) includes two displayportions 9803 and 9804. Note that the number of display portions of anelectronic device of one embodiment of the present invention is notlimited to two and can be one or three or more. In the case where anelectronic device includes a plurality of display portions, at least onedisplay portion includes the display device of one embodiment of thepresent invention.

FIG. 31(E) illustrates a laptop personal computer including a housing9821, a display portion 9822, a keyboard 9823, a pointing device 9824,and the like.

This embodiment can be combined with any of other embodiments asappropriate.

Example

In this example, the results of fabricating the display device of oneembodiment of the present invention and displaying an image will bedescribed.

The display device of this example is described with reference to FIG.6(B). The display device of this example includes a touch panel with atop-emission structure employing a color filter method as the displaypanel 10. The touch panel includes a light-emitting element and a touchsensor between a pair of flexible substrates. The thickness of thedisplay panel 10 is smaller than or equal to 100 μm. The display panel10 can be bent inward and outward.

The display panel 10 was manufactured by, in a manner similar to themanufacturing method of the structure example 1 described in Embodiment2, forming a layer to be separated on each of the two formationsubstrates, bonding the two formation substrates to each other,separating each formation substrate, and transferring the layer to beseparated between the pair of flexible substrates. Glass substrates wereused as the formation substrates. For the flexible substrate 51 and theflexible substrate 57, resin films were used. As a semiconductormaterial of the transistor, a CAAC-OS was used. As the light-emittingelement, an organic EL element was used. As the conductive layer 71, atitanium film with a thickness of 50 nm was used.

Under the display panel 10, a conductive film was placed. The conductivefilm includes an ITO film with a thickness of 100 nm over a PET filmwith a thickness of 127 μm. The ITO film corresponds to the conductivelayer 73.

FIGS. 32(A) and (B) show a conductive film placed over a housing. Overthe conductive layer 73 included in the conductive film, a conductor 74(a copper foil) is connected. A connection portion of the conductivelayer 73 and the conductor 74 was provided at a position which does notoverlap with the display panel 10. The wiring is soldered to theconductor 74. The wiring is led to GND of a power source. When theconductive layer 73 is in contact with the conductive layer 71 of thedisplay panel 10, the conductive layer 71 can be supplied with the GNDpotential.

FIG. 32(C) shows a photograph of a rear surface (surface on the sideopposite to the display surface) of the display panel 10. The conductivelayer 71 is provided over the flexible substrate 51. The conductivelayer 71 overlaps with the display region of the display panel 10 and isformed in a region larger than the display region.

FIGS. 33(A) and (B) show photographs of a display device displaying animage. In the display device shown in FIGS. 33(A) and (B), the displaypanel 10 can be folded in three parts by a housing, and the curvatureradius at that time is approximately 3 mm. The display panel 10 ispositioned to overlap with the conductive film so that the conductivelayer 71 is in contact with the conductive layer 73. As shown in FIGS.33(A) and (B), the display device of this example could performfavorable display both in the opened state and the folded state. Theconductive layer 71 was formed on the rear surface of the display panel10; however, there was no problem in display. In addition, even when thedisplay panel 10 was touched or the display panel 10 was bent, there wasno influence on display.

In this example, the conductive layer 71 was provided on the rearsurface of the display panel 10, and the conductive layer 71 wassupplied with the GND potential. Thus, even when the thickness of thedisplay panel 10 was thin enough to be subjected to repetitive bendingand unbending operation, noise from the outside could be reduced and thedisplay panel 10 could perform favorable display. In addition, theconductive layer 71 and the conductive layer 73 were not fixed; thus, adecrease in flexibility of the display panel 10 could be suppressed.Furthermore, the connection portion of the conductive layer 73 and theconductor 74 was provided at a position which does not overlap with thedisplay panel 10, whereby steps due to the connection portion were notformed in the display region, and a reduction in display quality couldbe suppressed.

REFERENCE NUMERALS

-   10 display panel-   11 first wiring-   12 second wiring-   13 third wiring-   14 fourth wiring-   15 fifth wiring-   16 display panel-   19 wiring-   20 layer including transistor-   21 conductive layer-   22 region-   22A region-   22B region-   22C region-   22D region-   31 light-emitting element-   32 transistor-   33 transistor-   34 capacitor-   39 capacitance-   41 electrode-   43 EL layer-   45 electrode-   51 flexible substrate-   53 insulating layer-   55 bonding layer-   57 flexible substrate-   60 electronic device-   61 housing-   65 band-   67 power storage device-   68 band-   71 conductive layer-   72 element layer-   73 conductive layer-   73 a conductive layer-   73 b conductive layer-   74 conductor-   74 a conductor-   74 b conductor-   81 display region-   82 scan line driver circuit-   83 FPC-   84 IC-   90 electronic device-   93 protective layer-   95 a support panel-   95 b support panel-   98 housing-   99 finger-   300 touch panel-   301 transistor-   302 transistor-   303 transistor-   304 light-emitting element-   305 capacitor-   306 connection portion-   307 conductive layer-   308 connection portion-   309 connector-   310 input device-   311 gate insulating layer-   312 insulating layer-   313 insulating layer-   314 insulating layer-   315 insulating layer-   316 spacer-   317 bonding layer-   318 input device-   319 connector-   320 touch panel-   321 electrode-   322 EL layer-   323 electrode-   324 optical adjustment layer-   325 coloring layer-   326 light-blocking layer-   326 a light-blocking layer-   326 b light-blocking layer-   327 insulating layer-   328 insulating layer-   330 flexible substrate-   331 electrode-   332 electrode-   333 electrode-   334 electrode-   341 wiring-   342 wiring-   347 region-   348 region-   349 region-   350 FPC-   351 IC-   355 conductive layer-   370 display panel-   371 flexible substrate-   372 flexible substrate-   373 FPC-   374 IC-   375 bonding layer-   376 insulating layer-   377 bonding layer-   378 insulating layer-   379 display panel-   380 conductive layer-   381 display portion-   382 driver circuit portion-   383 wiring-   385 connection portion-   386 connector-   387 crossing portion-   390 conductive layer-   391 bonding layer-   392 flexible substrate-   393 insulating layer-   395 insulating layer-   396 bonding layer-   398 separation film-   399 separation film-   401 formation substrate-   403 separation layer-   411 formation substrate-   413 separation layer-   723 back gate-   728 insulating layer-   729 insulating layer-   742 semiconductor layer-   743 gate-   744 a conductive layer-   744 b conductive layer-   747 a opening-   747 b opening-   747 c opening-   747 d opening-   772 insulating layer-   848 transistor-   7000 display portion-   7001 display portion-   7100 mobile phone-   7101 housing-   7103 operation button-   7104 external connection port-   7105 speaker-   7106 microphone-   7200 television set-   7201 housing-   7203 stand-   7211 remote controller-   7300 portable information terminal-   7301 housing-   7302 operation button-   7303 information-   7304 information-   7305 information-   7306 information-   7310 portable information terminal-   7320 portable information terminal-   7400 lighting device-   7401 stage-   7402 light-emitting portion-   7403 operation switch-   7410 lighting device-   7412 light-emitting portion-   7420 lighting device-   7422 light-emitting portion-   7500 portable information terminal-   7501 housing-   7502 tab-   7503 operation button-   7600 electronic device-   7601 housing-   7602 hinge-   7650 electronic device-   7651 non-display portion-   7700 portable information terminal-   7701 housing-   7703 a button-   7703 b button-   7704 a speaker-   7704 b speaker-   7705 external connection port-   7706 microphone-   7709 battery-   7800 electronic device-   7801 band-   7802 input/output terminal-   7803 operation button-   7804 icon-   7805 battery-   9700 automobile-   9701 car body-   9702 wheel-   9703 dashboard-   9704 light-   9710 display portion-   9711 display portion-   9712 display portion-   9713 display portion-   9714 display portion-   9715 display portion-   9721 display portion-   9722 display portion-   9723 display portion-   9801 housing-   9802 housing-   9803 display portion-   9804 display portion-   9805 microphone-   9806 speaker-   9807 operation key-   9808 stylus-   9821 housing-   9822 display portion-   9823 keyboard-   9824 pointing device

What is claimed is:
 1. A display device comprising: a flexiblesubstrate; a display region comprising a first conductive layer over afirst surface of the flexible substrate; a light-emitting element overthe first conductive layer; and a second conductive layer under a secondsurface of the flexible substrate; wherein the second conductive layeris electrically insulated from the first conductive layer, wherein thefirst conductive layer overlaps with the second conductive layer withthe flexible substrate provided therebetween, and wherein the secondconductive layer is supplied with a constant potential.
 2. The displaydevice according to claim 1, wherein the second conductive layer is incontact with a wiring supplied with the constant potential in a portionnot overlapping with the display region.
 3. The display device accordingto claim 1, wherein an area where the second conductive layer and thedisplay region overlap with each other is greater than or equal to 80%and less than or equal to 100% of an area of the display region.
 4. Thedisplay device according to claim 1, wherein an area of the secondconductive layer is larger than an area of the display region.
 5. Thedisplay device according to claim 1, wherein a capacitance is configuredto generate between the first conductive layer and the second conductivelayer.
 6. The display device according to claim 1, wherein the secondconductive layer comprises titanium.
 7. The display device according toclaim 1, wherein the light-emitting element comprises a first electrode,a light-emitting layer over the first electrode, and a second electrodeover the light-emitting layer, and wherein the second electrode issupplied with a constant potential.
 8. The display device according toclaim 1, wherein the display region is configured to be folded in twoparts.
 9. The display device according to claim 1, wherein the displayregion is configured to be folded in three parts.
 10. A display devicecomprising: a flexible substrate; a display region comprising a firstconductive layer over a first surface of the flexible substrate; alight-emitting element over the first conductive layer; a secondconductive layer under a second surface of the flexible substrate; and athird conductive layer under the second conductive layer, wherein thesecond conductive layer is electrically insulated from the firstconductive layer, wherein the first conductive layer overlaps with thesecond conductive layer with the flexible substrate providedtherebetween, wherein the third conductive layer is supplied with aconstant potential, and wherein the third conductive layer comprises aportion in contact with the second conductive layer and comprises aportion not fixed to the second conductive layer.
 11. The display deviceaccording to claim 10, wherein the second conductive layer is in contactwith a wiring supplied with the constant potential in a portion notoverlapping with the display region.
 12. The display device according toclaim 10, wherein an area where the second conductive layer and thedisplay region overlap with each other is greater than or equal to 80%and less than or equal to 100% of an area of the display region.
 13. Thedisplay device according to claim 10, wherein an area of the secondconductive layer is larger than an area of the display region.
 14. Thedisplay device according to claim 10, wherein a capacitance isconfigured to generate between the first conductive layer and the secondconductive layer.
 15. The display device according to claim 10, whereinthe third conductive layer comprises titanium.
 16. The display deviceaccording to claim 10, wherein the light-emitting element comprises afirst electrode, a light-emitting layer over the first electrode, and asecond electrode over the light-emitting layer, and wherein the secondelectrode is supplied with a constant potential.
 17. The display deviceaccording to claim 10, wherein the display region is configured to befolded in two parts.
 18. The display device according to claim 10,wherein the display region is configured to be folded in three parts.19. The display device according to claim 10, wherein the secondconductive layer comprises a metal.